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PRISCILA FERNANDES SILVA
INFLUÊNCIA DO TIPO DE ABRIGO E DA FREQUÊNCIA DE OFERTA
ALIMENTAR NO COMPORTAMENTO DO CAMARÃO Macrobrachium
rosenbergii (De Man 1879).
NATAL
2014
Tese apresentada a Universidade Federal do Rio
Grande do Norte, para obtenção do título de
Doutor pelo Programa de Pós-Graduação em
Psicobiologia.
PRISCILA FERNANDES SILVA
INFLUÊNCIA DO TIPO DE ABRIGO E DA FREQUÊNCIA DE OFERTA
ALIMENTAR NO COMPORTAMENTO DO CAMARÃO Macrobrachium
rosenbergii (De Man 1879).
NATAL
2014
Tese apresentada a Universidade Federal do Rio
Grande do Norte, para obtenção do título de Doutor
pelo Programa de Pós-Graduação em Psicobiologia.
Orientadora: Maria de Fátima Arruda de Miranda
Co-orientadora: Karina Ribeiro
AGRADECIMENTOS
Deixo aqui o meu agradecimento a todos que contribuíram direta ou
indiretamente para realização desse trabalho.
À minha família. Em especial ao meu pai José, minha mãe Célia e minha irmã
Fabíola, meus principais incentivadores, meus melhores exemplos, meus maiores
amores.
À minha orientadora, Profa. Maria de Fátima Arruda. Por toda sua paciência e
equilíbrio. Por sua visão prática e otimista. Por seu apoio e incentivo. Por todos os
ensinamentos teóricos e práticos sobre o comportamento animal, sobre ciência, sobre a
academia, sobre a Vida.
À minha co-orientadora Profa. Karina Ribeiro, pela disponibilidade e
colaboração.
Ao Prof. Arrilton Araújo, pelas orientações, discussões e pelos momentos
alegres no LBC.
A Thiago, meu companheiro de todas as horas, por seu apoio incondicional. E a
todos da família Miranda Moreira pelo carinho e incentivo.
A todos os colegas do Laboratório de Estudos do Comportamento do Camarão,
pela ajuda ao longo do trabalho.
A todos do Laboratório de Biologia Comportamental (LBC). Pelos momentos de
discussões, distrações e pelas amizades conquistadas.
Ao Prof. Francisco Seixas, por toda contribuição no meu aprendizado.
Ao Programa de Pós-Graduação em Psicobiologia, seus professores e
funcionários.
À CAPES e ao CNPq pelo apoio financeiro para o desenvolvimento dessa
pesquisa.
SUMÁRIO
RESUMO ....................................................................................................................... 1
ABSTRACT ................................................................................................................... 3
1. INTRODUÇÃO .......................................................................................................... 6
2. HIPÓTESES E PREDIÇÕES ................................................................................... 15
3. OBJETIVOS .............................................................................................................. 17
4. METODOLOGIA GERAL ...................................................................................... 18
4.1. Condição experimental .............................................................................. 18
4.2. Comportamentos registrados ...................................................................... 19
4.3. Relações de dominância .............................................................................. 19
5. MANUSCRITO 1 - Social status and individual behavioral differences in
Macrobrachium rosenbergii ………………………………………………………….. 20
6. MANUSCRITO 2 - Influence of shelter type on the behavior of Macrobrachium
rosenbergii (De Man 1879) juveniles. ……………………………………………….. 41
7. MANUSCRITO 3 - Behavior of Macrobrachium rosenbergii under diferent feeding
frequencies. ................................................................................................... ................ 60
8. DISCUSSÃO GERAL .............................................................................................. 77
9. CONCLUSÃO …………………………………………………………………….. 84
1
RESUMO
Macrobrachium rosenbergii é uma espécie de camarão de água-doce que apresenta
crescimento heterogêneo regulado por fatores sociais. É sabido que as condições de
viveiro podem intensificar o agonismo, causando danos aos animais, diminuição na
sobrevivência, além de gerar uma redução no seu bem-estar. Nosso objetivo foi
investigar o comportamento de M. rosenbergii na fase de juvenil em função de
diferentes tipos de abrigo e de frequência de oferta do alimento. Para isso, juvenis foram
observados em laboratório em três etapas. Na etapa I, caracterizamos o perfil
comportamental. Camarões foram mantidos em oito aquários (27 camarões/m²),
marcados e observados em quatro horários ao longo do dia para registro do
comportamento nas duas fases do ciclo de luz. Na etapa II (2 experimentos), avaliamos
a utilização de abrigos (tijolos ou rolo em tela de polietileno) pelos animais e sua
influência no agonismo. Para classificação dos animais no ranque de dominância o
método utilizado foi o David’s Score. Na etapa III (3 experimentos), avaliamos a
variação na frequência de oferta do alimento sobre o comportamento, em particular o
agonismo. Os resultados da etapa I mostraram que juvenis não apresentam um perfil
atividade/inatividade entre as fases do ciclo de luz, ou seja, os animais alternam
momentos de atividade nas duas fases do ciclo. Identificamos uma hierarquia social
com relações de dominância, na qual dominantes apresentaram vantagem no acesso ao
alimento e maior ganho de peso. Mesmo assim a frequência de ingestão do alimento não
diferiu entre dominantes e subordinados. Na etapa II, o tipo de abrigo influenciou o
comportamento. O abrigo de tijolo gerou uma maior frequência de permanência bem
como uma redução na frequência de interações agonísticas. Na etapa III, a distribuição
do alimento de forma mais frequente ao longo do dia, diminuiu a motivação dos animais
para a alimentação, bem como para o confronto. Desta forma, concluímos que a
2
utilização de abrigos que diminuam a detecção dos indivíduos pelos coespecíficos, bem
como o aumento na frequência de alimentação reduzem o agonismo. Tal resultado
acarreta numa melhora da qualidade de vida dos camarões e na sua qualidade como
produto final.
Palavras-chave: comportamento agonístico, ciclo de claro e escuro, juvenil, abrigo,
alimentação, bem-estar animal.
3
ABSTRACT
Macrobrachium rosenbergii is a freshwater prawn which presents agonistic behavior
and heterogeneous growth. It is known that captive conditions can intensify agonism
causing injuries and decreased survival, generating a condition of poor welfare. Based
on this, we aim to investigate the behavior of M. rosenbergii in the juvenile phase
according to different types of shelter and frequencies of feed offer, emphasizing their
agonistic behavior. For this, juveniles were observed in the laboratory in three steps. At
step I we characterized the behavioral profile; prawns were kept in eight aquariums (27
prawns/m2), identified and observed four times along both phases of 24 h light cycle. At
step II (2 experiments), we evaluated the use of shelters (brick or polyethylene rolls)
and their influence on agonism by the animals. For classification of animals in
dominance rank, the method used was David's Score. At step III (3 experiments), we
evaluated different frequencies of feed offer on the behavior of individuals, in particular
agonism. Results showed that juveniles do not present a pattern activity/inactivity
between the phases of the light cycle. We identified a dominance hierarchy among
individuals taking advantage of access to food by the dominant, which showed greater
weight gain although the frequency of intake did not differ between individuals. The
type of shelter influenced the behavior of animals. Brick shelter generated a higher
frequency of permanence and a reduction in the frequency of agonistic interactions. The
distribution of food more frequently throughout the day, decreased the motivation of
animals for food, as well as to fight. Prawns fed four times showed lower frequency of
feed intake and agonistic interactions. Thus, we conclude the shelters which reduce
animal’s detection by coespecifics and offer the food four times along the day reduce
agonistic behavior. This result causes na improvement in life quality of the prawns and
also in its quality as final product.
4
Keywords: agonistic behavior, light cycle, juvenile, shelter, feeding, welfare.
5
APRESENTAÇÃO
Essa tese será apresentada na forma de três manuscritos. Iniciaremos o texto com
uma introdução geral que dará base para as discussões específicas de cada manuscrito.
Seguinte à introdução geral, descrevemos a metodologia geral que engloba os aspectos
comuns dos três manuscritos.
O manuscrito 1, intitulado “ Social status and individual behavioral differences
in Macrobrachium rosenbergii ”, discute o perfil de atividades do camarão na fase de
juvenil, enfatizando as diferenças individuais e as relações de dominância.
O manuscrito 2, intitulado “ Behavior of Macrobrachium rosenbergii under
different feeding frequencies ”, avalia o comportamento do camarão submetido a três
diferentes frequências de oferta do alimento.
O manuscrito 3, intitulado “Influence of shelter type on the behavior of
Macrobrachium rosenbergii (De Man 1879) juveniles”, avalia o comportamento do
camarão associado a dois diferentes tipos de abrigo.
Por fim, apresentamos uma discussão geral destacando os resultados mais
relevantes do trabalho.
6
1. INTRODUÇÃO
Macrobrachium rosenbergii é uma espécie de camarão de água doce bastante
conhecida mundialmente. Espécies do gênero Macrobrachium estão distribuídas nas
zonas tropicais e subtropicais do planeta e podem ser encontradas em lagos, rios,
pântanos e áreas estuarinas. M. rosenbergii é uma das maiores espécies do gênero, é
nativa do Sul e Sudeste da Ásia, bem como do Norte da Oceania e de ilhas ocidentais do
Pacífico (New, 2002). Apesar de passar a maior parte do seu ciclo de vida na água doce,
pode ser considerada uma espécie dependente de estuário, já que precisa de água salobra
para se reproduzir (Loebmann, Mai & Lee, 2010). É uma espécie resistente a condições
adversas e por isso se tornou a espécie de camarão de água doce mais utilizada em
cultivos no mundo (Iketane et al. 2011). Atualmente pode ser encontrado em todos os
continentes e no Brasil é a espécie de água-doce predominantemente cultivada (New
2000; Valenti 2007).
Dentre as principais características de M. rosenbergii podemos destacar a
variedade de tamanhos entre os indivíduos de uma população, principalmente entre
machos adultos (Karplus, 2005). Numa população sexualmente madura desta espécie
podemos encontrar três morfotipos de macho, os quais diferem nas suas características
morfológicas, fisiológicas e comportamentais. Os machos de quela azul, que possuem
quelas longas, azuis e espinhosas; machos de quela laranja, que apresentam quelas de
tamanho intermediário, sem espinhos e geralmente laranjas, podendo ter partes azuis; e
por fim os machos pequenos que tem suas quelas pequenas, finas e claras (Barki,
Karplus & Goren 1991a). Barki, Karplus e Goren (1991b) registraram a formação de
uma hierarquia de dominância entre estes morfotipos, onde o macho de quela azul é
dominante em relação ao macho de quela laranja, que por sua vez, domina o macho de
7
quela pequena. Esta ordem dos morfotipos na hierarquia provavelmente está relacionada
ao tamanho dos indivíduos, o que é comum entre crustáceos. Diferenças na morfologia
de machos adultos podem ser observadas em diferentes espécies e geralmente estão
associadas à escolha de parceiros durante a reprodução. Em crustáceos a presença de
machos grandes com apêndices, como quelípedes bem desenvolvidos, sugere a
monopolização das fêmeas durante seu período receptivo (Thiel, Chak & Dumont,
2010). Segundo Sagi e Ra’anan (1985) a estratégia reprodutiva de machos de M.
rosenbergii difere entre os morfotipos e o macho de quela azul alcança maior sucesso
no acesso e guarda das fêmeas e também na fertilização.
O tamanho do indivíduo nesta espécie parece ser um dos fatores mais importantes
na determinação do seu papel no contexto social, mas não só o tamanho corporal. Barki,
Karolus e Goren (1992) classificaram machos de M. rosenbergii de quela laranja e azul
em três tamanhos: grande, médio e pequeno. Os pesquisadores então distribuíram os
animais em grupos de seis indivíduos com um representante de cada morfotipo e
tamanho. Os resultados mostraram que machos de quela azul sempre dominavam os
machos de quela laranja, mesmo quando tinham comprimentos de corpo semelhantes.
Os autores então consideraram o comprimento das quelas e observaram que machos
pequenos de quela azul dominavam machos grandes de quela laranja quando a
assimetria entre as quelas era pequena. Desta forma o estudo aponta o efeito do
morfotipo como principal determinante na hierarquia, já que este efeito levaria em conta
não só o tamanho das quelas, mas também suas diferenças de coloração, que também é
um indicador de status social em outras espécies.
Em juvenis de M. rosenbergii há evidências de uma diferenciação na taxa de
crescimento entre os indivíduos. Ra’anan e Cohen (1984) observaram que juvenis
mantidos em grupo, após um período de tempo, apresentam duas classes de tamanho
8
diferentes: os saltadores que apresentam uma taxa excepcional de crescimento e os
retardatários que surgem na presença dos saltadores e apresentam crescimento bastante
reduzido. Estes animais que cresceram mais e mais rapidamente provavelmente se
tornarão machos de quela azul ou laranja após a maturação sexual, já os retardatários se
desenvolveriam em machos de quela pequena. Os autores também observaram animais
mantidos em isolamento, os quais apresentaram uma taxa de crescimento mais
homogênea ao longo do tempo. Estes resultados levaram os autores a apontar o controle
social ao invés da variação genética, como maior força atuante sobre as taxas de
crescimento na espécie.
De acordo com Karplus (2005) quatro mecanismos sociais podem ser apontados
como reguladores do crescimento em crustáceos: a competição direta por alimento -
onde indivíduos dominantes ou mais agressivos acessariam primeiro o alimento
impedindo que os demais o consumissem; supressão do apetite - após a formação de
uma hierarquia de dominância aqueles indivíduos subordinados teriam uma taxa de
ingestão menor mesmo com alimento abundante no ambiente; eficiência de conversão
do alimento diferenciada – os subordinados teriam uma taxa de conversão alimentar
pouco eficiente; e por fim o aumento da atividade locomotora – subordinados passariam
mais tempo se deslocando na tentativa de escapar dos dominantes e gastariam assim
mais energia. Todos estes mecanismos envolvem interações agonísticas entre os
animais. Em adultos de M. rosenbergii, pesquisas já mostram que o macho de quela
azul tem prioridade no acesso aos recursos (Sagi & Ra’anan, 1985; Barki et al., 1992).
Em juvenis ainda há pouca informação sobre como as diferenças individuais atuam
na população. Animais jovens ainda não apresentam morfotipos, mas diferenças nas
taxas de crescimento já podem ser observadas nesta fase, as quais podem se manter até a
fase adulta. E ainda que discretas estas diferenças podem acarretar na formação de uma
9
hierarquia de dominância entre os indivíduos. Brown et al. (2003) observaram grupos
de quatro animais juvenis de M. rosenbergii em laboratório. Os pesquisadores
caracterizaram as interações agonísticas, as relações de dominância e subordinação, a
consistência destas relações ao longo do tempo e como estas interações estariam
relacionadas com as taxas metabólicas latentes dos indivíduos no momento da formação
do grupo. Dentro dos grupos estudados foi possível observar a formação de uma
hierarquia onde um ou dois indivíduos eram dominantes e os demais subordinados.
Entretanto esta hierarquia não era linear, na maioria dos casos um subordinado recebia a
maior parte das agressões. O índice de dominância dos indivíduos não sofreu alterações
ao longo do tempo. Os animais mostraram uma tendência maior a perder nos conflitos
no dia anterior a ecdise, mas o seu índice era rapidamente restabelecido em no máximo
dois dias após a muda.
Como dito anteriormente M. rosenbergii é a espécie de camarão de água doce mais
cultivada atualmente. Os dados atuais sobre o cultivo desta espécie mostram o uso de
diferentes estratégias de criação. M. rosenbergii tem sido cultivado em viveiros de
cimento ou terra, em gaiolas, plantações de arroz e em policultivo com diferentes
espécies de peixe de água doce (New, 2002; Hossain & Kibria, 2006; Cuvin-Aralar,
Aralar, Laron & Rosario, 2007; Uddin et al., 2009). A densidade populacional nestes
cultivos também varia e em viveiros e gaiolas tende a ser mais alta (Cuvin-Aralar et al.,
2007). Com relação a densidade populacional, três tipos de sistema podem ser
encontrados: extensivo, semi-intensivo e intensivo. O cultivo extensivo utiliza baixa
densidade de animais (1 – 4/m²), geralmente é feito em reservatórios ou campos de
arroz, o alimento artificial não é utilizado, nem são feitas fertilizações. O cultivo semi-
intensivo é o mais comum em zonas tropicais, a densidade populacional é mais alta (4 –
20/m²), o viveiro é fertilizado e a ração é ofertada como complementação do alimento
10
natural, a qualidade da água e mortalidade dos animais é monitorada. O sistema de
cultivo intensivo é feito em viveiros de terra ou concreto, onde os animais são estocados
a uma densidade igual ou maior que 20/m². Este tipo de sistema exige altas taxas de
renovação de água, aeração constante, ração nutricionalmente completa e
monitoramento rigoroso da qualidade de água (New, 2002).
Densidades populacionais mais altas do que a natural podem interferir na expressão
comportamental dos indivíduos e no seu desenvolvimento. Algumas técnicas tem sido
utilizadas para auxiliar o cultivo em altas densidades. O uso de substratos verticais tem
minimizado os impactos negativos da densidade em algumas espécies, o que pode se
dever ao aumento na produção de alimento natural agregado a estes substratos no
viveiro, ou a maior disponibilidade de espaço para os indivíduos (Moss & Moss, 2004;
Arnold et al., 2006a). O uso de telas verticalmente distribuídas ou canos de PVC em
tanques de cultivo contribuiu para o maior crescimento e sobrevivência de P. monodon
submetido à altas densidades, quando comparado com os tratamentos sem adição de
substrato (Arnold, Sellars, Crocos & Coman, 2006a; Arnold, Coman, Jackson & Grove,
2009). Tidwell e Coyle (2008) testaram o uso de diferentes tipos de tela no cultivo de
M. rosenbergii. Os resultados não diferiram entre os tipos de tela utilizados, mas, que o
peso médio dos camarões foi 41 % maior nos tratamentos com as telas e a produção de
kg/ha foi 80% melhor. Os autores apontam que a adição de substrato permitiria que os
camarões se mantivessem separados uns dos outros, o que diminuiria as interações
intra-específicas e o estresse. Segundo Baird, Paullo e Macmillan (2006) a
complexidade do habitat reduz o número de interações entre os indivíduos através da
diminuição na percepção do coespecífico.
O uso de abrigos é um método que pode reduzir as interações agonísticas entre
indivíduos. Entretanto se o abrigo for um recurso limitante no ambiente o efeito pode
11
ser contrário (Baird et al., 2006). De qualquer forma o abrigo é um recurso importante
para crustáceos, por isso seu uso tem sido considerado para aquicultura e alguns
trabalhos apontam de fato seu efeito na diminuição das interações agonísticas. M
australiense como outras espécies do gênero apresenta a formação de uma hierarquia de
dominância, onde o dominante defende seu território atacando o subordinado que se
aproximar e o subordinado por sua vez, evita o dominante. Para que esses
comportamentos ocorram é preciso que os indivíduos possam detectar a presença do
outro. Baseando-se nesta predição, Lammers, Warbutton e Cribb (2009b) observou que
a disponibilidade de refúgio reduziu a resposta dos indivíduos dominantes a presença
dos subordinados, o que consequentemente diminuiria as interações entre eles. García-
Guerrero e Molina (2008) distribuíram juvenis de M. americanum em duas diferentes
densidades populacionais com e sem abrigo (98 camarões/m² com e sem abrigo e 196
camarões/m² com e sem abrigo). Tubos de plástico (15 cm) serviram como abrigo. Os
resultados mostraram que a presença do abrigo aumentou a sobrevivência e favoreceu o
crescimento dos animais. O melhor resultado foi encontrado na densidade 98
camarões/m² com abrigo, onde provavelmente a competição por espaço e alimento foi
menor. Os autores também apontam que o abrigo permite que os animais se protejam
após a ecdise.
Crustáceos em geral apresentam uma diferença na distribuição das suas atividades
entre as fases de claro e escuro do ciclo de 24 h. Muitas espécies se mostram mais ativas
durante a noite. Durante o dia o risco de predação é maior e o que observamos são
diferentes estratégias entre as espécies para evitar o predador. No camarão
Farfantepenaeus subtilis o comportamento de enterramento é o mais freqüente na fase
de claro do ciclo de luz (Silva, Medeiros, Silva & Arruda, 2012). Já em L. vannamei a
inatividade é o comportamento predominante na fase de claro enquanto a natação
12
predomina na fase de escuro (Pontes, Arruda, Menezes & Lima, 2006).
Macrobrachium australiense passa a maior parte da fase de claro inativo e em áreas de
vegetação, o que diminuiria sua exposição a possíveis predadores (Lammers et al.,
2009a). Há pouca ou nenhuma informação na literatura sobre o ritmo de atividades
exibido por M. rosenbergii ao longo do dia. Provavelmente esta espécie deve apresentar
o mesmo padrão de outras espécies de palaemonídeos, que reduzem sua atividade e
aumentam o uso do refúgio durante o dia (Lammers, Warbuttin & CRibb, 2009b). Tão
pouco se sabe como o padrão de atividades se mantém em função da presença de
coespecíficos ou da disponibilidade de alimento.
O manejo do alimento é um importante fator na produção, eficiência na
conversão do alimento e diminuição do desperdício, daí a necessidade de
desenvolvimento de estratégias baseadas no comportamento alimentar do animal
(Zheng, Dong & Tian, 2008). Crustáceos em ambiente natural se alimentam de uma
variedade de organismos como bactérias, plâncton, algas, sedimento, moluscos, peixes e
outros crustáceos (Figueiredo & Anderson, 2009). Nas fazendas de cultivo desses
animais o regime de alimentação varia em função da espécie, da densidade e da fase de
vida do animal, dentre outros fatores. Nos sistemas de cultivo semi-intensivo e
intensivo, principalmente com espécies de camarão marinho, o alimento artificial é
utilizado como complemento ao alimento natural e a oferta é feita em bandejas
distribuídas ao longo do viveiro. É através destas bandejas que a avaliação do consumo
do alimento é feita. Se não há sobras na bandeja, a taxa de alimentação deve aumentar,
mas se houver sobras, a quantidade de ração para a próxima oferta deve diminuir (New,
2002). Esta forma de manejo alimentar é amplamente utilizada, embora seja feita de
forma empírica, não levando em conta características comportamentais dos animais
(Pontes & Arruda, 2005 a, b).
13
O alimento artificial representa aproximadamente 55% do custo operacional em
cultivos de camarão. Práticas apropriadas de manejo do alimento maximizam o
crescimento e sobrevivência dos camarões, enquanto o manejo incorreto leva a uma
produção subótima, promove o surgimento de enfermidades e problemas na qualidade
da água que afetam negativamente a produção, bem como os ecossistemas adjacentes
(Mohanty, 2001). A atenção dirigida ao manejo alimentar é crescente, entretanto,
aspectos relacionados ao comportamento frente as práticas atuais, ainda é pouco
investigado. Aguzzi, Company e Sardá (2004) afirmam que o perfil de alimentação
exibido pela espécie pode ser o resultado de interações complexas entre o seu ritmo
comportamental e características moduladoras do ambiente.
M. rosenbergii torna-se onívoro ao longo do seu desenvolvimento. Após o
estágio larval os animais passam a ser menos seletivos e exploram os recursos
alimentares disponíveis no ambiente (Barros & Valenti, 1997). A maior parte dos
estudos sobre alimentação de M. rosenbergii estão voltados para alimentação de larvas,
as necessidades nutricionais da espécie e as práticas utilizadas nos sistemas de
policultivo. A obtenção destas informações e sua a plicabilidade tem permitido o
sucesso de M. rosenbergii na atividade. Mas alguns aspectos permanecem pouco
conhecidos. Não há dados, por exemplo, sobre o comportamento do animal frente a
oferta do alimento, melhores horários de alimentação ou diferenças na resposta
alimentar entre as fases do ciclo de 24 h. Tão pouco há informações sobre o impacto da
freqüência de oferta do alimento no comportamento de juvenis.
Lima, Pontes e Arruda (2009) submeteram L. vannamei a três diferentes
frequências de oferta do alimento (três, quatro e sete vezes) ao longo de sete horários
fixos durante o dia. A ingestão foi mais frequente quando a oferta foi feita três vezes ao
dia, principalmente as 12 e 14 h. Quando o alimento era ofertado sete vezes os camarões
14
passaram a maior parte do tempo inativos. Segundo Pontes, Lima e Arruda (2008) a
latência de chegada a bandeja e de ingestão do alimento, em juvenis de L. vannamei, foi
menor quando o alimento era ofertado três vezes ao dia. Os autores também registraram
as latências quando a oferta foi feita quatro e sete vezes. O ganho de peso foi
semelhante nos animais alimentados três e quatro vezes e maior do que naqueles onde a
oferta foi feita sete vezes. Smith, Buford, Tabrett e Ward (2002) registraram o
crescimento e a sobrevivência de P. monodon, mantidos em tanques e alimentados três,
quatro, cinco ou seis vezes ao dia. Os resultados não mostraram diferença significativa
nos parâmetros observados entre as freqüências. Nhan, Wille, Hung e Sorgeloos (2010)
investigaram a resposta de M. rosenbergii em estágio larval, alimentados duas ou seis
vezes ao dia com náuplios de Artemia. A freqüência mais alta de oferta levou a um
desenvolvimento mais rápido das larvas. Segundo os autores ofertar o alimento várias
vezes ao dia garante que ele esteja sempre disponível no ambiente.
O estudo do comportamento tem se mostrado um importante aliado na elaboração
do manejo adequado de espécies mantidas em cativeiro. M. rosenbergii é uma espécie
de interesse comercial que possui características peculiares, como a heterogeneidade no
crescimento e o comportamento agressivo. Entretanto, pouco é sabido sobre a resposta
comportamental dos juvenis à oferta do alimento e a densidade populacional elevada
numa condição artificial, bem como do papel do abrigo nesta condição. Esta pesquisa
busca agregar tais informações ao conhecimento já existente sobre a espécie,
colaborando para a otimização do seu manejo.
Além disso, é crescente a necessidade de considerar o bem-estar dos indivíduos,
respeitar suas necessidades e garantir seu crescimento de maneira saudável. Mais uma
vez reforçamos o papel da investigação comportamental para alcançar esse objetivo. Só
15
assim, poderemos ter como resultado, um melhor aproveitamento na produção e melhor
qualidade de vida para animais como decorrência da aplicação desses conhecimentos.
16
2. HIPÓTESES E PREDIÇÕES
Hipótese 1: Há diferenças no acesso ao alimento e no crescimento entre indivíduos
dominantes e subordinados. (Artigo 1)
Predição 1: dominantes apresentarão maior frequência de chegada à bandeja e de
ingestão do alimento e ganho de peso quando comparados aos indivíduos subordinados.
Predição 2: a latência de chegada à bandeja e de consumo do alimento será menor para
os dominantes.
Predição 3: indivíduos subordinados exibirão frequências mais altas de atividades
associadas à locomoção, como natação, rastejamento e exploração, acarretando em
maior gasto energético e menor ganho de peso.
Hipótese 2: como as demais espécies de crustáceos, M. rosenbergii apresenta
diferenças no perfil de atividades entre as fases de claro e de escuro do ciclo de 24
horas.
Predição 1: atividades relacionadas à locomoção são mais frequentes na fase de escuro
(Artigo 1).
Predição 2: as interações agonísticas são mais intensas na fase de escuro, já que os
comportamentos de ritualização/avaliação seriam pouco eficientes nesta fase (Artigo 1).
Predição 3: os animais permanecem inativos na fase de claro; havendo disponibilidade
de abrigo, M. rosenbergii passará a maior parte da fase de claro nesses locais
(Manuscrito 2).
17
Hipótese 3: o tipo do abrigo (tijolo ou rolo feito com tela) interfere no seu uso pelo
animal e no comportamento de Macrobrachium rosenbergii (Manuscrito 2).
Predição 1: a frequência de permanência no abrigo será mais alta quando os camarões
estiverem associados ao abrigo de tijolo, uma vez que as características deste material
(coloração escura, barreira entre as câmaras) são mais atrativas para os animais.
Predição 2: a frequência de interações agonísticas será mais baixa no abrigo de tijolo
quando comparado ao abrigo de tela.
Hipótese 4: a oferta do alimento modifica a expressão dos comportamentos em
Macrobrachium rosenbergii (Manuscrito 3).
Predição 1: considerando o limite fisiológico da espécie, espera-se que quanto maior a
frequência de oferta alimentar, maior a frequência de ingestão desse alimento.
Predição 2: comportamentos relacionados à busca e captura do alimento serão mais
frequentes nos horários em que o alimento for ofertado.
Predição 3: as interações agonísticas devem diminuir à medida que a oferta do alimento
for mais frequente, já que alguns indivíduos vão se saciar nas primeiras ofertas e não
competirão pelo recurso nas demais.
18
3. OBJETIVOS
3.1. Objetivo geral
Caracterizar o comportamento de Macrobrachium rosenbergii em função de: diferentes
tipos de abrigo e diferentes frequências de oferta alimentar.
3.2. Objetivos específicos
- Caracterizar o comportamento de Macrobrachium rosenbergii juvenis nas fases de
claro e de escuro do ciclo de 24h.
- Verificar a existência de hierarquia de dominância em juvenis.
- Verificar se a posição do indivíduo na hierarquia de dominância interfere no
comportamento.
- Verificar se a posição na hierarquia de dominância afeta o crescimento dos juvenis.
- Verificar se o tipo de abrigo interfere no seu uso pelos camarões.
- Analisar como o tipo de abrigo interfere na distribuição de atividades comportamentais
desses animais.
- Analisar como o tipo de abrigo interfere nas interações agonísticas.
- Comparar a distribuição de atividades comportamentais em três diferentes frequências
de alimentação.
- Avaliar como a frequência da oferta do alimento interfere nas interações agonísticas.
19
4. METODOLOGIA GERAL
4.1. Condição experimental
Esta pesquisa foi desenvolvida no Laboratório de Estudo do Comportamento de
Camarão, localizado no Departamento de Fisiologia da UFRN. Os animais utilizados
nos experimentos foram obtidos de larvicultura comercial ainda no estágio de pós-larva
e transferidos para viveiros na Escola Agrícola de Jundiaí – UFRN, localizada no
município de Macaíba – RN. Os animais permaneceram lá até atingirem o estágio
juvenil, quando foram transportados para o laboratório. As unidades experimentais
utilizadas foram aquários (50 x 30 x 40 cm) com aproximadamente 30 L de água, para
as etapas I e II. Para a etapa III foram utilizados aquários maiores (100 x 50 x 60 cm)
com aproximadamente 200 L de água. Todos os aquários continham substrato de areia,
aeração constante e sistema fechado de recirculação de água através de filtros
biológicos. Os filtros são constituídos por camadas sucessivas de: lã de vidro, areia de
granulometria maior, areia de granulometria menor, conchas de ostras, lã de vidro, areia
de granulometria maior, areia de granulometria menor e carvão ativado. O alimento
utilizado foi ração comercial peletizada, no equivalente a 10% da biomassa, ofertada em
bandejas.
O laboratório é dividido em duas salas, ambas com sistema de luz artificial e
fotoperíodo controlado de 12 h, uma delas apresentando a fase de claro das 06:00 às
18:00 e escuro das 18:00 às 06:00 e a outra sala sob ciclo de luz invertido apresentando
a fase de escuro das 07:00 às 19:00 e claro das 19:00 às 07:00. Isto permite que os
aquários sejam observados nas fases de claro e escuro. Para observação no escuro uma
luminária com lâmpada vermelha (15 W) foi utilizada. O atraso de uma hora entre as
fases possibilitou que um observador realizasse o registro em todas as janelas de
20
observação, nas duas fases do ciclo de luz. A qualidade da água foi monitorada e os
parâmetros físico-químicos mantidos nos níveis ideais para a espécie.
4.2 Comportamentos registrados
Os comportamentos característicos do perfil de atividades foram: exploração,
rastejamento, natação, ingestão do alimento, limpeza, parado e cavando (Silva et al.,
2012). Os comportamentos agonísticos registrados ao longo das observações, foram
adaptados de Barki et al. (1991) sendo eles: afastar (AFA), flexão abdominal (FABD),
aproximar (APF), perseguir (PER), estender quelípedes (EQUE), estender o meru
(EME), levantar o corpo (LEV), golpear (GOLP), abraço (ABR), atacar (ATA), atacar
com dáctilos (ATADACT). Durantes as interações agonísticas também foi registrado
quais eram os animais envolvidos e a duração em segundos da interação.
4.3 Relações de dominância
Como Macrobrachium rosenbergii é uma espécie que apresenta uma hierarquia
de dominância entre os indivíduos de um grupo, nós testamos como essa hierarquia se
estabelece nas duas densidades populacionais. O método utilizado foi o David’s Score,
que calcula o ranque de dominância de um indivíduo baseado nos resultados das suas
interações com os outros indivíduos do grupo.
Os aspectos específicos da metodologia de cada experimento serão apresentados
no seu respectivo manuscrito.
21
5. ARTIGO 1 - Social status and individual behavioral differences in
Macrobrachium rosenbergii.
Priscila Fernandes Silva* and Maria de Fátima Arruda
Departamento de Fisiologia, Universidade Federal do Rio Grande do Norte, 59078-
970, Natal, RN, Brazil.
Aceito: Marine and Freshwater Behavior and Physiology.
Abstract
Adult Macrobrachium rosenbergii males appear in three distinct morphotypes
associated with dominance hierarchy. Juveniles can also differ but only in body size.
We examined whether juveniles present a size-related dominance hierarchy and whether
it could be related to individual behavioral profile. Behaviors were recorded in groups
of four prawns for 30 days in the laboratory, four times during light and dark phases of
the 24 h cycle. Dominance ranks were analyzed using David’s score method. Observed
behaviors differed between light phases. In most groups, two individuals obtained a
positive score and the other two a negative score; they were therefore considered
dominants and subordinates respectively. There was no correlation between dominance
and general behavioral activities. Dominants had greater weight gain and faster access
to food. The precocious relation between growth and dominance suggests dominant
juveniles are more likely to become blue claw adult males, the morphotype with greater
reproductive success.
Keywords: prawn, Macrobrachium rosenbergii, juvenile, agonistic behavior, activity
profile, dominance hierarchy, feeding, growth
22
Introduction
Before sexual differentiation in the prawn species Macrobrachium rosenbergii, juvenile
prawns present distinct growth rates. Two types of juveniles can be observed in a
population, the jumpers and the laggards. Jumpers have higher growth rates and will
probably become orange claw and blue claw males. Laggards demonstrate slow growth
and mostly become small males as adults (Ra’anan & Cohen 1984, Karplus et al. 1987).
In M. rosenbergii, evidence suggests that social factors play a major role in
heterogeneous growth (Ra’anan & Cohen 1984).
Four social mechanisms may act as growth regulators in crustaceans: direct
competition, appetite suppression, altered food-conversion efficiency and increased
motor activity (Karplus 2005). All mechanisms are mediated by agonistic interactions
between individuals. In direct competition, more aggressive or dominant individuals
have an advantage in acquiring food. In appetite suppression, subordinate individuals
ingest less food in the presence of dominants, smaller individuals have less efficient
food conversion and subordinate animals have higher levels of locomotor activity to
avoid dominant individuals (Cobb et al. 1982, Karplus et al. 1992, Karplus 2005).
Agonistic behavior is a fundamental component of resource acquisition. In
crustaceans, as in other species, intrinsic and extrinsic factors affect the result of
aggressive interactions (Bergman & Moore 2003). Body size can play a major role in
determining the outcome of competition (Lammers et al. 2010). It may thus serve as an
honest signal of an individual’s competitive ability and can affect status within a
population. During competition, larger individuals have a greater chance of acquiring
and maintaining resources over time (Wacker et al. 2012). In addition, it was observed
that individuals in some species increase their growth rate after acquiring dominant
positions in the group (Nakano 1995, Heg et al. 2004, Riebli et al. 2011). They may
23
then suppress the growth of smaller individuals (Karplus 2005). Thus we can predict a
positive feedback mechanism that reinforces individual positions in a dominance rank
order.
Numerous studies in recent years have revealed wide variability in the behavior of
individuals of the same species, even of the same breed and reared under the same
conditions (Sih et al. 2004, Miranda-de la Lama et al. 2011, Hoogenboom et al. 2013).
Aggressive behavior and dominance can be associated with other characteristics of
individual behavior. Such differences in a behavior result in differences in their
reproductive success and, consequently, in fitness (Dingemanse & Réale 2005, Alvaréz
& Bell 2007).
Most studies in M. rosenbergii have addressed adult agonistic behavior or
management. There is little knowledge about the behavioral profile and activity
distribution of juveniles in this species. There is also a lack of comprehensive
information on how these factors integrate and influence the social status of the
individual in the population. Animals do not differ from one another in the juvenile
phase with respect to the morphotype but differ in size. In some groups, this difference
is very subtle. Previous studies have already shown differences in the outcomes of
agonistic interactions between individuals (Brown et al. 2003).
Based on the above information it is important to investigate whether individual
juveniles differ in the expression of behavior and how these differences might interfere
with their development and life history.
M. rosenbergii is largely used nowadays in research and also in aquaculture.
However there is still a lack of information about the juvenile phase. For example, what
is the relevance of agonistic behavior during this phase and how is it distributed across
the day? Most available data have focused in adult behavior and in the difference
24
between morphotypes. Our goal here was therefore to characterize the behavioral
activity profile of juvenile Macrobrachium rosenbergii, to establish a dominance rank
order among individuals and to test for a relationship between dominance status and the
behavioral activity profile. We also compared growth rates among individuals with
different dominance scores. Our hypothesis was that the dominance hierarchy would
influence the expression of individual behavior. We postulated that subordinates would
spend more time in locomotor activity. We also predicted that dominant juveniles would
have greater access to food and higher food ingestion (as demonstrated in adults, Barki
et al 1992) and would also have faster growth rates than subordinate individuals.
Methods
Experimental animals and conditions
Macrobrachium rosenbergii were obtained from a commercial hatchery while they were
still in the post-larval stage. The post-larvae were distributed in external tank nurseries.
At two months old, 32 prawns were transferred to the laboratory, where they were
weighted and distributed in eight aquaria (50 x 30 x 40 cm) with approximately 30 liters
of water, sand substrate, constant aeration and a closed system of water recirculation
through biological filters. No shelters were provided for the animals. The average initial
weight was 1.7 ± 0.9 g and the body length was 6.4 ± 1.0 cm. The four prawns placed
together in an aquarium did not differ in weight by more than 5%. Animals were housed
uder 32W white fluorescent light on a 12 h controlled photoperiod for the light phase
and 15W red fluorescent light for the dark phase. The light sources were distributed
evenly across the laboratory. To characterize the behavioral profile throughout the 24 h
cycle, four aquaria were distributed in a room submitted to an artificial light cycle
25
equivalent to natural light (light phase from 06:00 to 18:00 and dark phase from 18:00
to 06:00). The others were exposed to an inverted light cycle in another room (light
phase from 19:00 to 07:00 and dark phase from 07:00 to 19:00). This difference of one
hour between cycles allowed a single observer to record the behaviors. Physicochemical
parameters were monitored to control water quality. Temperature was measured with a
glass thermometer (Jad BT02; Jad Aquarium, Guandong, China) and maintained at 24.8
± 0.8ºC. To measure the dissolved oxygen we used Dissolved oxygen - Marine and
Freshwater Test (Labcon tests, Camboriu, Brazil) the mean and standard deviation were
7.7 ± 0.8 mg L-1
. For pH and ammonia the tests used were pH Test – Freshwater and
Toxic Ammonia – Freshwater (Labcon Tests, Camboriu, Brazil) The pH was
maintained at 7.4 ± 0.2 and ammonia at 0.0 mg L-1
.
Data collection
The prawns were allowed to acclimatize to laboratory conditions and artificial light
cycles for 10 days before recording started. Observations were made for five days per
week, four times per day at one, four, seven and ten hours for 30 days after the
photoperiod transition. Aquaria submitted to a light regime equivalent to a natural light
cycle were observed only in the light phase whereas aquaria submitted to an inverted
cycle were observed in the dark phase. There was a difference of one hour in the
transition between phases in the rooms with different light cycles. This difference
allowed a single observer to record the behavior of the animals. Behavior was recorded
using two methods: 1) the instantaneous focal animal method to record behaviors
related to the behavioral activity profile and 2) the continuous focal animal method to
record agonistic behaviors. Observations lasted 15 min per aquarium with instantaneous
data recorded each minute. This means that every minute / sample instant the behavior
26
displayed by each prawn was recorded. Individuals were differentiated by natural
marks. Prawns were fed twice a day with commercial shrimp feed one and seven hours
after the photoperiod transition for both phases and immediately before the behavioral
recordings were taken. Food was placed in trays and removed only before the next
feeding time. The amount of food offered was equivalent to 10% of the total biomass.
Behaviors related to the behavioral activity profile were adapted from an
ethogram of other species of shrimp (Silva et al. 2012). The following categories were
recorded:
(1) exploring the substrate - during which the prawn uses its pereopod chelae to
investigate the substrate - the animal may be stationary or moving;
(2) pellet ingestion - during which the prawn uses its pereopod chelae to handle
and eat a pellet;
(3) inactivity - during which the animal remains stationary on the substrate;
(4) burrowing - during which the prawn uses its pereopod chelae and pleopods
to remove the substrate and form a cavity in which it remains afterwards;
(5) swimming - during which the prawn moves horizontally or vertically in the
water column;
(6) crawling - during which the prawn moves along the substrate;
(7) auto-grooming - during which the prawn uses its pereopod chelae to groom
the body.
Exploring the substrate, swimming and crawling are behavioral components of
locomotor activity.
Agonistic behaviors were adapted from an ethogram that describes behaviors of
M. rosenbergii adults (Barki et al. 1991a). We recorded the following behaviors:
(1) approach – when one prawn moves toward another;
27
(2) move away - when one prawn moves away from another;
(3) rush - rapid movement of one prawn towards another;
(4) abdomen flexing - rapid flexion of the abdomen which results in a movement
upwards and backwards through the water (also known as a tail flick or flip);
(5) cheliped extension - parallel forward extension of both chelipeds towards
another prawn;
(6) meral spread - an elevated body position during which both chelipeds are
raised horizontally with the merus spread perpendicular to the body;
(7) complete lifting - oblique lifting of both the chelipeds and the anterior part of
the body;
(8) scissoring - the rapid bringing together of the two claws in a scissoring
motion on the body of another prawn;
(9) embrace - one prawn embraces another prawn with its chelipeds;
(10) push - one prawn pushes one of its chelae against the body of another
prawn;
(11) chase - one prawn chases the other with its chelipeds extended.
Immediately after feed offer we recorded the latency to accessing the feeding
tray and the latency to beginning food ingestion for each individual. At the end of the
experiment, the prawns were weighed again to determine their weight gain. Prawns that
died during the experiment were only replaced if death occurred within five days of the
beginning of the experiment. Mortality occurred only in the last week of data collection
when ten prawns died.
Data analysis
28
Agonistic interactions within each group of four animals were analyzed to establish the
dominance rank order. The method used was the David's Score method, which ranks
each animal according to agonistic interactions between all individuals in the group,
taking into account the proportion of wins and losses of each individual and the
weighted proportion of wins and losses of the individuals against the animals with
which they have interacted (Gammel et al. 2003, Bang et al. 2010). An individual was
classified as a “winner” when the opponent exhibited the “move away” response after a
mutual approach and interaction. The retreating prawn was classified as a “loser”.
A Kolmogorov-Smirnov test showed that the data was not distributed normally
so a Kruskal-Wallis test was used to compare the frequencies of the different behaviors.
When significant differences were found the post-hoc Multiple Comparisons test was
applied. The Mann-Whitney test was used to analyze differences in behavior between
light cycle phases. The Spearman’s correlation was used to correlate individual
dominance scores with the frequencies of behaviors, weight gain and the number of
times an animal arrived at the food tray. The weights of the animals and the latencies
are presented as the mean and standard deviation. The significance level was set at p
<0.05. Correlations were considered significant when Spearman’s r values were equal
or greater than 0.5.
Results
Behavioral activity profile and agonistic behavior
Auto-grooming and exploration were the most frequent behaviors without a significant
difference between them and burrowing was the least frequent (H = 115.023, df = 6, p ˂
0.05). Other behaviors did not show differences in their frequencies when compared
29
with one another. When the two light phases were compared, ingestion (U = 48590.5, p
> 0.05) and burrowing (U = 92.05, > 0.05) did not differ from one phase to another.
Exploration (U = 416854.5, p < 0.001) and auto-grooming (U = 496984.5, p < 0.001)
were more frequent in the light phase. Crawling (U = 128299.5, p < 0.05), swimming
(U = 446984.5, p < 0.05) and inactivity (U = 79254.5, p < 0.05) were more frequent in
the dark phase (Fig 1).
Cheliped extension was the most frequent of the agonistic behaviors (H =
138.69, df = 10, p ˂ 0.05). The behavior of move away (U = 22550.0, p < 0.001) was
more frequent in the light phase when the light cycle phases were compared. Approach
(U = 499625.4, p ˂ 0.05), abdomen flexing (U = 15650; p ˂ 0.05) and push (U =
17072.50; p ˂ 0.05) behaviors were more frequent in the dark phase.
Regarding the observed latencies, the average time prawns took to reach the feed
tray in the light phase was 125 ± 180 s. In the dark phase it was 137 ± 165. The average
time to consume food was 156 ± 190 s during the light phase and 174 ± 191 s in the
dark phase of 24 h light cycle. The average final weight of prawns was 2.0 ± 0.9 g.
Fig. 1. Relative frequency of behaviors components of behavioral activity profile.
30
Dominance score and behavioral activity
The David's score of each individual was obtained within each observed group. Most
groups presented the same pattern with two positive and two negative scores (Table 1).
To establish whether there is a relationship between locomotor activity and dominance
score, correlation tests were applied to the behaviors of exploration, crawling and
swimming. The rs results obtained were: exploration (rs = 0.07, p ˂ 0.05), crawling (rs =
0.17, p ˂ 0.05), swimming (rs = -0.14, p ˂ 0.05) and so not significant.
No correlation was found between the frequency of feed ingestion and David's
score (rs= 0.439; p ˂ 0.05). Significant correlations were found between the animal’s
score and weight gain (rs = 0.51, p ˂ 0.05) (Fig.2) and the number of times the animal
arrived at the feeding tray (rs = 0.55, p ˂ 0.05) (Fig.3).
Table 1. David’s score result for each animal per aquarium.
Aquarium Animal
1 2 3 4
A 5,84 1,77 -2,06 -3,61
B 3,9 0,54 -1,09 -1,81
C 5,05 0,27 -1,22 -1,51
D 3,17 1,9 -0,32 -3,06
E 5,5 -0,2 -1,95 -2,03
F 5,48 1,72 -2,36 -3,92
G 5,13 -0,19 -0,25 -3,26
H 5,29 0,67 -1,18 -3,12
31
-4 -3 -2 -1 0 1 2 3 4 5 6
Weight Gain (g)
-6
-4
-2
0
2
4
6
8
Da
vid
's S
co
re
Fig.1 Spearman correlation between animal’s dominance score and weight gain (rs = 0,51, p ˂ 0,05)
-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26
Feeding Tray Arrived
-6
-4
-2
0
2
4
6
8
Da
vid's sco
re
Fig. 2 Spearman correlation between animal’s dominance score and number of times animal arrived
on feeding tray (rs = 0,55, p ˂ 0,05)
32
Discussion
The results obtained did not show a clear pattern of activity/inactivity distribution
between the light and dark phases of the day. We also were not able to identify a
relationship between the behavioral activity profile and individual status on dominance
hierarchy.
Auto-grooming was the most observed behavior in M. rosenbergii juveniles and
it occurred mainly in the light phase. Grooming is a behavior used to clean body parts in
decapod crustaceans as a defense against fouling organisms (Bauer 1989, Bauer 2002,
Barr et al. 2008). Time spent on this behavior varies among species. Auto-grooming is
more frequent in species with a migratory life cycle such as those in the
Macrobrachium genus. Changes between environments may increase grooming
pressures, typically in animals exposed to freshwater and marine fouling agents (Maurik
& Wortham 2011). It would therefore be advantageous to the individual to groom
frequently. The juvenile animals also exhibited high frequencies of exploration. This
behavior is an important component of the search for food and environmental
recognition, and exploration often involves animal movement (Patullo & Macmillan
2005, Lima et al. 2009). In Farfantepenaeus subtilis, also during juvenile phase, the
highest level of exploration coincided with the highest intake of food, despite the fact
that the behavior did not differ between light phases (Silva et al. 2012).
Swimming and crawling were exhibited more often during the dark phase;
inactivity also followed this pattern. Food intake did not differ between phases, which
means that prawns respond to food any time it is offered. This pattern was also observed
in other species (F. subtilis and L. vannamei) exposed to artificial conditions. Behaviors
such as exploration and crawling also show elevated levels during the offering of food,
33
and this trend is independent of the light phase (Pontes & Arruda 2005, Silva et al.
2012). Macrobrachium borelli exhibits increased foraging at night in its natural
environment and this is associated with high general activity during this phase (Collins
1997).
Chelae extension was the most common among agonistic behaviors. This
behavior is characterized by the absence of physical contact between individuals. The
chelae are often involved in communication in crustaceans, especially in agonistic
behaviors (Mariappan et al. 2000). In M. rosenbergii, the positioning and movement of
the chelae have great importance in agonistic interactions (Barki et al. 1991a). Their
movement and positioning are components in the ritualization of conflict, an efficient
way of avoiding direct confrontations that could cause damage to both opponents. Many
species use signals, usually low intensity activities, at the beginning of an interaction.
At this point, the individual can evaluate its opponent and decide whether to retreat or
escalate (Gareth & Elwood 2009).
When we compare agonistic behavior between light phases, approach, push and
abdominal flexion were more frequent in the dark phase, whereas the behavior move
away was more often displayed in the light phase. Abdominal flexion is an avoidance
behavior, which allows the animal to move away quickly and to a greater distance from
the opponent, so it is associated with a situation with a high aggressive component
(Patullo et al. 2009). Push behavior is characterized by the fast movement of an
individual towards another. The higher frequency of these behaviors in the dark phase
could be related to situations in which there are elevated levels of aggression. Visual
communication is potentially compromised during the dark phase with a concomitant
reduction in the efficiency of visual displays. In consequence the conflict could evolve
faster to more intense levels.
34
Classification obtained through David's score showed differences in the social
rank of individuals within the groups in our lab. In most aquariums, two individuals
obtained a positive score and were therefore considered dominants; the other two
obtained negative scores and were considered subordinates. There was a great
difference between the prawns in first and second rank positions. Using a dominance
index that was calculated daily, juvenile M. rosenbergii showed a similar distribution in
a group of four individuals, with one dominant, one intermediate and two subordinates
(Brown et al. 2003).
Our hypothesis proposed that juveniles of Macrobrachium rosenbergii would
differ in some aspects of their behavioral activity profile and those differences would be
related to dominance hierarchy. We expected that subordinates would spend more time
performing locomotor activities and that dominants would be more successful at food
acquisition and gain weight faster. These results partially corroborated our hypothesis.
Exploration, swimming and crawling are components of locomotor activity in
prawns. None of these behaviors showed a meaningful correlation with individual
dominance scores. In crustaceans, increased energy expenditure on locomotor activity is
a factor observed in subordinate individuals. This can reduce their growth rate (Karplus
2005). Our results did not show the influence of this factor in M. rosenbergii juveniles.
There was also no substantial correlation between an individual’s level of food
consumption and its dominance score. On the other hand, weight gain and feed tray
arrival presented a meaningful and positive correlation with individual dominance
score. The similar level of food acquisition among prawns was probably due to food
availability once a sufficient amount of food was offered for all individuals so that it
remained in the tray until the next food offering. Despite the fact that the dominants
arrived first to the tray, they did not remain there for a long period of time, thereby
35
allowing access by other prawns. Although no metabolic measurements were made in
this study, our results corroborate the mechanism of altered food-conversion efficiency
for heterogeneous growth in crustaceans (Karplus et al. 1992).
Behavioral differences among individuals have been observed in aggression and
activity levels, site fidelity, shelter use and dominance status (Sih et al. 2004, Lammers
et al. 2009, Hoogenboom et al. 2013). A correlation between some of these factors has
also been recorded. For example, higher locomotor activity was recorded in Homarus
americanus subordinates when compared to dominant individuals (Cobb et al. 1982).
Few papers discuss the role of dominance hierarchy in M. rosenbergii juveniles.
Most studies on this topic have been conducted in adult animals in which morphotype
differentiation has already taken place. In juveniles, the hierarchy is not related to
morphotype, so factors such as size and weight must play this role. In this work, we did
not test the animals in a condition in which there was competition for resources, since
food was offered in large quantities. Also, there were no shelters in the aquaria and
prawns were not yet in the reproductive stage with a need to compete for mates. An
experimental design with a competitive component could lead to different responses.
Nevertheless, agonistic behavior and dominance hierarchy are important aspects in the
whole life history of M. rosenbergii. It is known that juveniles that grow faster have
more chance to become a dominant blue claw male which is the morphotype with
higher reproductive success.
Our results showed that in juvenile individuals there was a relationship between
growth and dominance, so this individual profile emerges early in the individual
development. When used in aquaculture, individuals spend most of their juvenile phase
in the ponds. Their behavior may thus impact on management strategy.
36
Acknowledgements
We would like to thank the Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), the Coordenação de Aperfeiçoamento de Pessoal de Nível
superior (CAPES) and the Department of Physiology of the Universidade Federal do
Rio Grande do Norte for their support in developing this study.
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41
6. MANUSCRITO 2 - Influence of shelter type on the behavior of Macrobrachium
rosenbergii (De Man 1879) juveniles.
Priscila Fernandes Silva, Karina Ribeiro, Maria de Fátima Arruda.
Manuscrito a ser submetido (Aquaculture Research)
Introduction
Macrobrachium rosenbergii is an important species for aquaculture worldwide.
However this species has some features that can affect negatively the success of
production. They present aggressive behavior and heterogeneous growth; in a juvenile
population we can observe two types of individuals: the jumpers, with higher growth
rates and the laggards, with slower rates of growth (Ra’anan and Cohen, 1984; Karplus
et al., 1987). When adults, males can differ in three morphotypes defined based on
morphological, physiological and behavioral characteristics. Females do not present
morphotypes (Barki, Karplus and Goren, 1991a, b). Agonistic behavior, competition
and dominance are the main social factors influencing the heterogeneous growth (Cobb,
Tamm and Wang, 1982; Karplus, Hulata and Zafrir, 1992; Karplus, 2005).
The adopted stocking density is a critical factor for the success of the
production, once it can improve the final result of the production cycle but also is
related with a higher incidence of cannibalism and heterogeneous growth in freshwater
prawns (Cuvin-Aralar, Aralar, Laron & Rosario 2007; García-Guerrero & Molina 2008;
Moraes-Valenti, Morais, Preto & Valenti 2010). Among the strategies to improve
captive environment, the addition of artificial substrates and shelters has been an
important tool in the reduction of negatives effects of population density, improving
42
growth rates and survival. Studies show that this is due to factors such as physical
separation of animals, increased growth area for natural food, reducing time spent in
agonistic interactions and the intensity of these interactions (García-Guerrero & Molina
2008; Tidwell & Coyle 2008; Cenni, Parisi and Gherardi , 2010). The most common
type of added substrate is panels of polyethylene commonly used as construction/safety
fence (Tidwell, 2003). To provide shelters to prawns different types of material have
been used, such as bricks, pvc pipes, plants and tires (Muthy, Kumarswamy, Palaksha,
Sujatha and Shankar, 2012). Added substrate and shelters present different advantages.
Artificial substrates increase the available surface area and shelters can also be used as a
substrate in addition to providing a place for animals to hide. However, this kind of
material could interfere with harvest (New, 2002).
Species of genus Macrobrachium including M. rosenbergii in natural
environment are found associated with rocks and vegetation. Shaded areas and obstacles
prevent detection and protect against predators besides avoiding interactions with
conspecifics (Kutty and Valenti, 2010). In this sense, the choice of a shelter by the
individuals depends on certain features such as space to hide, color and surface area
(Mariappan & Balasundaram, 2003; Shivananda, Kumarswamy, Palaksha, Sujatha and
Shankar, 2012). Behavior has repercussion on survival prospects; the best time and
context to perform a particular behavior depends on the costs and benefits associated
with that and other behaviors (Cuthill and Houston, 1997). Differences in behavior
distribution i.e. behavioral routine are related to environment characteristics such as
resource availability, light cycle, time schedule, habitat complexity, intraespecific
competition and presence of predators (Cenni, Parisi and Gherardi, 2010; Lammers,
Warburton, and Cribb, 2010; Silva, Medeiros, Silva and Arruda, 2012). Sheltering
behavior is a component of behavioral routine of M. rosenbergii, and can be influenced
43
by shelter availability, competition and shelter structure as well as influence the
exhibition of other behaviors.
In many aspects, the environment of a farm is different from the natural
environment. So even though the species has a high potential to adapt to the condition
of captivity, the absence or exacerbation of certain stimuli can alter the expression of
behaviors and affect negatively the development of animals. Another important aspect
to be considered is the animal’s welfare. A production can be considered sustainable
when supplies the needs of the animals resulting in good welfare (Broom, Galindo and
Murgueitio, 2013). Vertebrates and terrestrial species have received more attention in
this area, but the interest in welfare of invertebrates including crustaceans has been
increased (Bekoff, 2007; Broom, 2007).
Shelters are consistently used in intensive nursery systems and in some grow-out
ponds (Karplus and Sagi, 2010). However there is still limited information about how
shelter type influences the behavior of prawns. So our aim is to characterize the
behavior of Macrobrachium rosenbergii juveniles associated with two different types of
shelters, with emphasis on agonistic behavior and compare differences between time
schedules and light phases.
Methods
Animals and laboratory conditions
Macrobrachium rosenbergii, in the post-larval stage, were obtained from a commercial
hatchery and distributed in external tank nurseries. At two months old, 64 juveniles
were transferred to the laboratory. For each experiment were used eight aquariums (50 x
30 x 40 cm) with approximately 30 liters of water, sand substrate, constant aeration and
44
a closed system of water recirculation through biological filters. The aquariums received
four prawns each (27 prawns/m²). Animals were housed in artificial lighting in a 12 h
controlled photoperiod with white fluorescent light bulbs (32W) for the light phase and
red fluorescent light bulbs (15 W) for the dark phase. To characterize the behavioral
profile throughout the 24 h cycle, four aquariums were submitted to an artificial light
cycle equivalent to natural light (light phase from 6:00 am to 6:00 pm and dark phase
from 6:00 pm to 6:00 am) and the others were exposed to an inverted light cycle (light
phase from 6:00 pm to 6:00 am and dark phase from 6:00 am to 6:00 pm). Aquariums
were divided into four quadrants (1, 2, 3 and 4) using vertical lines drawn 12.5 cm apart
on the front surface of the glass. An imaginary line in the middle of the aquarium
separated the front and back halves of the structure totalizing eight quadrants. The
spatial position of each individual was recorded during behavioral observations to
measure its movement. After recording their weights, the prawns were allowed to
acclimatize to artificial conditions for 10 days before observations for each treatment
started.
Experimental design
To compare the effect of two different types of shelter we conducted two experiments.
For each type of substrate eight aquariums were used, half maintained at light cycle and
the other half in the inverted cycle. Before the period of observation animals were
weighted and marked with color tags on their carapace for individual observation. The
tag was lost during ecdisis, but was placed back after two days. The animals were
observed over a 30 days period, interspersed, totaling 10 days of observation for each
treatment. Observations occurred four times per day: one, four, seven and ten hour after
photoperiod transition; and lasted 10 min per aquarium with instantaneous record at
45
each minute. Behavior was recorded using two methods: instantaneous focal animal
method to record behaviors related to the behavioral activity profile and continuous
focal animal method in order to record agonistic behaviors. Agonism was also recorded
through instantaneous focal method, if the behavior occurred at the sampling instant.
Prawns were fed twice a day, one and seven hours after photoperiod transition, for both
phases, immediately before behavioral recordings. Food was placed in trays and
removed only before the next feeding time. The amount of ration offered was equivalent
to 10% of the total biomass.
Behaviors related to the behavioral activity profile were adapted from an
ethogram of other species of shrimp (Silva, Medeiros, Silva and Arruda, 2012). The
following categories were recorded: (1) exploring the substrate, when the prawn uses
pereopod chelae to investigate the substrate, stationary or moving; (2) pellet ingestion,
the prawn uses pereopod chelae to handle and ingest the pellet; (3) inactivity, the animal
remains stationary on the substrate; (4) burrowing, the prawn uses pereopod chelae and
pleopods to remove the substrate and form a cavity, where it remains afterwards; (5)
swimming, the prawn moves horizontally or vertically in the water column; (6)
crawling, the prawn moves along the substrate; (7) auto-grooming, the prawn uses
pereopod chelae to groom the body. Exploring the substrate, swimming and crawling
are behavioral components of locomotor activity. Agonism was also recorded when the
interaction happened at the moment of register. Agonistic behaviors were adapted from
an ethogram that describes behaviors of M. rosenbergii adults (Barki et al., 1991a). We
recorded the following behaviors: (1) approach, when one prawn moves toward another;
(2) move away, when one prawn moves away from another; (3) rush, expressed as rapid
movement of one prawn towards another; (4) abdomen flexing, rapid flexion of
abdomen which results in a movement upwards and backwards through the water; (5)
46
cheliped extension, parallel forward extension of both chelipeds towards another prawn;
(6) meral spread, an elevated body position while both chelipeds are raised horizontally
with the merus spread perpendicular to the body; (7) complete lifting, oblique lifting of
both the chelipeds and the anterior part of the body; (8) scissoring, the rapid bringing
together of the two claws in a scissoring motion on the body of another prawn; (9)
embrace, one prawn surrounds another prawn with its chelipeds; (10) push, one prawn
pushes one of its chelae against the body of another prawn; (11) chase, one prawn
chases the other with their extending chelipeds. To obtain the displacement frequency of
each prawn we recorded the frequency each prawn changed the position over the period
of observation. At the end of each experiment prawns were weighted again to obtain
weight gain.
Brick shelter
In this experiment the eight aquariums received one brick with four holes (diameter: 9.5
cm; lenght: 3.5 cm) (Fig. 1). The shelter was placed randomly in the substrate. During
observation we recorded if the prawns were in the shelter.
Polyethylene tubes
For this experiment we uses tubes made of panels of polyethylene (diameter: 9.5 cm;
lenght: 3.5 cm), commonly used as security fence (Fig.1). Each aquarium received four
tubes distributed one per quadrant. During observation we recorded if the prawn were in
the shelter.
47
Data analysis
According to Kolmogorov-Smirnov normality test, the data did not show a normal
distribution. Mann-Whitney test was used to compare permanence between shelter
types, behaviors distribution between shelter types and also to compare frequency of
permanence in the shelter between light cycle phases. Kruskal-Wallis test was used to
compare behaviors between time schedules in each treatment. When significant
differences were found the post-hoc Multiple Comparisons test was applied.
Significance level of p < 0.05 was adopted for all the tests.
Agonistic interactions between each group of four animals were analyzed to
establish the dominance rank order. The method used was David's Score, which ranks
each animal according to agonistic interactions between all individuals in the group
taking account the number and the result of interaction between dyads (Gammel, De
Vries, DouMnhall, Carlin and Hayden, 2003). Spearman’s correlation was used to
correlate individual dominance score with frequency of permanence in the shelter by the
animal. The significance level was p <0.05. Correlations were considered significant
when Sperman’s rs were equal or greater than 0.5.
Fig. 1. From left to right: materials used as shelter and its distribution in experimental
aquariums.
48
Results
In this study we intended to verify if animals differ in the use of two different types of
shelter. To answer this question we analyzed the frequency of permanence in each
shelter type, differences between light phases and behavioral activities. We also
investigated individual differences in frequency of permanence according to prawn’s
position in a dominance rank. The results showed that prawns used brick shelter in a
significantly higher frequency than fence shelter (Mann-Whitney test, U = 762981.0, P
˂ 0.001) (Fig. 2).
For each type of shelter we compared permanence between light and dark
phases of 24 h cycle. Animals in aquariums with fence shelter used it more during the
light phase (Mann-Whitney test, U = 182299.0, P ˂ 0.05). But when living with brick
shelters permanence was higher at night (Mann-Whitney test, U = 192996.0, P ˂ 0.05).
We also observed differences in the schedules along the day, but only to fence shelter.
The difference was observed between the first time of the light phase and the first time
Fig. 2. Frequency of shelter use between treatments. Different letters indicate
statistical differences (P ˂ 0.05).
Median
25%-75%
Min-Max Brick Fence
Shelter type
-2
0
2
4
6
8
10
12
Fre
qu
en
cy o
f sh
elte
r use
a b
49
of dark phase, and also between the third time of light phase and the first time of dark
phase; one hour after the photoperiod transition to dark phase animals presented the
lowest frequency of permanence (Kruskal-Wallis test, H = 28.62027, P ˂ 0.05). For
brick shelter no difference was observed (Kruskal -Wallis test, H = 7.999331; P ˃ 0.05).
The recorded behaviors differed in its distribution between types of shelters.
Behaviors such as crawling (Mann-Whitney test, U=685151.5, P ˂ 0.05) and swimming
(Mann-Whitney test, U=686804.0, P ˂ 0.05) were more frequent when prawns were
using brick shelters. Exploration (Mann-Whitney test, U=655998.0, P ˂ 0.05), feeding
(Mann-Whitney test, U=672326.5, P ˂ 0.05) and auto-grooming (Mann-Whitney test,
U=602536.0, P ˂ 0.05) presented higher frequencies in treatment with fence shelter.
Inactivity (Mann-Whitney test, U=730469.0, P ˃ 0.05) and burrowing (Mann-Whitney
test, U=749016, P ˃ 0.05) did not differ between treatments. We also obtain animal’s
displacement in the aquarium through the record of its position in the aquarium every
minute of the period of observation. The frequency of displacement was higher when
prawns were associated with fence shelter.
Agonistic behavior was recorded through two methods. During the ten minutes
period of observation we recorded agonism using the continuous focal animal method,
but during the instantaneous record if prawns were involved in an agonistic interaction
it was also recorded. Agonism was more frequent in the treatment with fence shelter
through instantaneous method (Mann-Whitney test, U=732140.0, P ˂ 0.05) and also
through continuous method (Mann-Whitney test, U= 41667.0, P ˂ 0.05) (Fig. 3).
50
After data collection each prawn was ranked inside their group according to
David’s score. We verify if prawns position influence the use of shelter by them. The
results showed a positive correlation between permanence in fence shelter and
individual David’s score (rs = 0.073612, P ˂ 0.05); the same was obtained between
brick shelter and David’s score (rs = 0.103701, P ˂ 0.05). However, since the rs value
was too low we did not considered the correlation significant.
Discussion
The two types of chosen materials differed in their characteristics and
consequently was expected influence the behavior of individuals in a different way. The
results confirmed our hypothesis; we recorded a higher frequency of permanence of
prawns in brick shelter. There are two possible factors that can explain this result, which
are not mutually exclusive. The first is that the bricks used were of brown color
generating a dark area where animals could remain. M. rosenbergii has a preference for
dark substrates, which could be related to a preference of reduced levels of reflected
Median
25%-75%
Min-Max Brick Fence
Shelter type
-2
0
2
4
6
8
10
12
Fre
qu
en
cy o
f ag
on
ism
(co
ntin
uo
us fo
ca
l an
ima
l me
tho
d)
a
b
Fig. 2. Frequency of agonistic behavior between shelter types. Different letters
indicate statistical difference (P ˂ 0.05).
51
light and/or a perception of dark colors as a refuge zone (Juarez, Holtschmit, Salmeron
and Smith, 1987; Mariappan & Balasundaram, 2003). For another species of the genus,
Macrobrachium nobilii, darkness is important for habitat selection by the animal. Both
adults and juveniles preferred dark shelters than light colored ones and never used
transparent shelters (Mariappan & Balasundaram, 2003).
Another possible factor is that prawns present a preference for certain
characteristics of this material, including color, which may be due to its efficiency to
prevent the detection of individuals by their conspecifics and predators. Crustaceans
vary in the strategies used to avoid predators and agonistic encounters with others.
Among the most common strategies are burying in the substrate, use of refuge areas and
decreased activity at certain times of the day (Nunes, Goddarg and Gesteira, 1996;
Lammers, Warburton and Cribb, 2009). Data shows that Macrobrachium species fit in
the last two strategies (Mariappan & Balasundaram, 2003; Lammers, Warbuton and
Cribb, 2009). The refuge areas used do not always offer a shelter; rocks and vegetation,
in particular, increase habitat complexity and impede the detection of the individual by
others. Visual and chemical communication plays a major role in interactions between
individuals in many species of crustaceans, including M. rosenbergii (Juarez,
Holtschmit, Salmeron and Smith, 1987). Objects inserted in the tank can block or
redirect these signals in water. Once the prawn cannot find another individual, the
interaction between them will not occur (Cenni, Parisi and Gherardi, 2010). This is in
agreement with our results, which show a decrease in the frequency of agonistic
interactions in aquariums with bricks as shelter. Brick can act as a more effective
blocker of cues dissemination than fence.
Prawns differ in use of shelter between light phases. When associated with fence
shelter, prawns used more the shelter during the light phase of 24 h cycle. With brick,
52
shelter use was higher at dark phase. This result confirms the impact of shelter type on
prawn behavior. The way behavioral activities are distributed along the day varies
between species ranging from those with an activity profile completely opposite
between the light and dark phases to those species that have a similar frequency of
behaviors between phases.
Age is another factor which influences activity levels and use of shelter
(Mariappan and Balasundaram, 2003; Balasundaram, Jeyachitra and Balamurugan,
2004). M. nobilii and M. malcolmsonii spent more time in shelter during the light
phase, however juveniles spent more time outside when compared to adults. Shelter
type also influences its behavior, i.e. time spent within shelter was higher when it was
pvc pipes than when it was tiles in both phases of daily cycle of 24 h (Balasundaram,
Jeyachitra and Balamurugan, 2004).
Besides sheltering behavior, other behavioral activities varies according to
shelter type. Crawling behavior and swimming were more frequent when prawns used
bricks as shelters. Displacement, exploration, auto-grooming and feeding presents
higher frequency in presence of fence shelter. Inactivity and burrowing did not differ
between shelter types. Despite behaviors such as crawling and swimming involved
movement of animal, displacement was lower in presence of brick shelter, which
indicated that the animal tends to remain in a more restricted area of the aquarium,
without changing its quadrant. Lobsters, Homarus americanus, in the presence of
pieces of concrete bricks spent more time stationary near shaded areas produced by the
bricks (Cenni, Parisi and Gherardi, 2010). M. rosenbergii using fence shelter exhibit
higher levels of displacement and exploratory behavior. Environment exploration can be
related to reducing the vulnerability of the animal. In areas with low quality refuge, M.
australiense explored the habitat more frequently. When vulnerable, it is advantageous
53
for the animal quickly identify potential hazards present in that environment, improving
their chances of survival (Lammers, Warburton and Cribb, 2009).
Another possible explanation for our result of exploratory behavior is associated
with our result of feeding. The unfilled structure of fence shelter allows the chemical
stimulus of the ration to spread more efficiently in aquarium. Studies have identified a
relationship between these behaviors, once during exploration the prawn use its
pereopods to scavenging the substrate where it can find the food (Lima, Pontes and
Arruda, 2009; Silva, Medeiros, Silva and Arruda, 2012).
The effects of habitat complexity and shelter availability can be distinct. An
object placed in the tank could increase environment complexity without providing
shelter for the animals. Studies have demonstrated the role of habitat complexity in
reduces agonistic interactions, but some of these studies point out that habitat
complexity alone can generate this result. Once shelter is an important resource, fights
for access will be common (Baird, Patullo and Macmillan, 2006; Lammers, Warburton
and Cribb, 2009). In our study, bricks produced a better result than fence shelter in
reducing the frequency of agonistic interactions, probably by the combination of shelter
availability and increase in habitat complexity. To evaluate possible differences in
shelter use between individuals, each prawn received a position in a dominance rank,
within their group, through David’s score method. After that a test was carried out to
verify if there was a correlation between prawn’s position with frequency of shelter use,
nonetheless no correlation was found. This result can be related with developmental
stage of prawns. Juveniles tend to be more active than adults in many species of
crustaceans, and spend less time in refuges or shelters (Kenyon, Loneragan and Hughes
1995; Balasundaram, Jeyachitra and Balamurugan, 2004; Silva, Medeiros, Silva and
Arruda, 2012). Shelter is important to attract mates and can be a more valuable resource
54
for animals in reproductive stage. Furthermore the number of shelters available was
sufficient for all the prawns in the aquarium, even though at no time we observed all
shelters occupied.
Added substrates can increase the production of benthic species since they use a
two dimensional area and there will be more space for the animals, reducing the
negative effects of population density and agonistic behavior (Tidwell, Coyle and
Schulmeister 1998; Arnold, Sellars, Crocos, German and Coman, 2006; Daly, Swingle
and Eckert, 2009). But, besides added substrate, we confirmed in this study the
importance of shelter availability and the need for attention in the selection of shelter
type. Once the characteristics of the chosen material can affect animal’s behavior.
Many studies have reported the harmful effects of some management practices
that farming systems currently use. The more commonly chosen species are those that
have increased resistance to such effects. However these species also has a limit, which
has been continuously tested in management. Inappropriate strategies can generate
stress and injuries, affecting growth and survival. To produce a captive condition with
higher welfare is necessary to know the species, their physiology and behavior. Interest
in the welfare of invertebrates has grown over the years. But there is still a need for
information on the species kept in captivity so that appropriate measures are taken.
Higher welfare conditions can be achieved through methods such as environmental
enrichment. In this sense we emphasize shelter use in M. rosenbergii breeding, mainly
brick shelter, once it can increase habitat complexity and reduce agonistic interactions
allowing the development of the animal with better quality of life.
55
Acknowledgements
We would like to thank the Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), the Coordenação de Aperfeiçoamento de Pessoal de Nível
superior (CAPES) and the Department of Physiology of the Universidade Federal do
Rio Grande do Norte for their support in developing this study.
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60
7. MANUSCRITO 3 – Behavior of Macrobrachium rosenbergii under diferent feeding
frequencies.
Priscila Fernandes Silva, Karina Ribeiro, Maria de Fátima Arruda.
Manuscrito a ser submetido ( Applied Animal Behaviour Science)
1. Introduction
One of the main mechanisms by which animals acquire resources is aggression. Body size
is usually associated with the outcome of aggressive interactions and therefore with the capacity
of an individual to acquire and maintain a resource (Moore, 2007; Yoshino et al., 2011). In M.
rosenbergii, evidence suggests that social factors such as competition and dominance play a
major role in heterogeneous growth. These social mechanisms are based on agonistic
interactions between individuals (Cobb et al., 1982; Karplus et al., 1992; Karplus, 2005).
Agonistic interactions between individuals can result in loss to the production, due to damages
caused to the animals and decrease survival and this may lead to growth rate variations and
other culture inefficiencies.
The availability of limiting resources, as food, can potentially influence the intensity of intra
and interspecific interactions (Duarte et al., 2010). Food distribution in the environment varies.
It can be found clumped or dispersed in time and space. Resources dispersal in time could lead
to a change in the type of competition observed, from exploitation competition to interference
competition, with higher levels of aggression (Bryant and Grant, 1995; Goldeberg et. al., 2001).
The existence of a dominance hierarchy is another factor influencing competition for food.
Dominant animals have advantage in accessing food, they can defend and monopolize it
keeping the subordinates away from food patches through agonistic behaviors (Weir et al.,
2004). Intraspecific competition can result in damage and mortality (Wenngren and Ólafsson,
2002).
61
In farming systems the way food is distributed, i.e. feed amount, feeding times and
frequency are determined mostly by farmer’s operational criteria. This practice does not
consider important aspects of species physiology and behavior (Pontes et. al., 2008). Feed
management is an important aspect of farming once that implies high costs if performed
improperly resulting in water quality deterioration, environmental pollution and poor welfare
for animals (Mohanty 2001, Smith et al., 2002). The frequency which the ration is offered is a
relevant component of feeding management. Many researches tested and suggest different
feeding frequencies to different species or even to the same one (Velasco et al., 1999; Smith et
al., 2002; Lima et al., 2009). The marine shrimp Litopenaeus vannamei fed three, four or seven
times a day shows a frequency of ingestion inversely proportional to the number of daily
feedings (Pontes et al., 2008). In other condition it was observed a positive effect on shrimp
growth when feed frequency was increased (Tacon et al., 2002). Many studies discuss feeding
strategies for M. rosenbergii, however most of the discussion is focused on the type of food and
the quantity supplied, but not on feeding frequency. Feed offered more times along the day can
reduce the animal’s hunger or the motivation to feed. In individuals kept in captivity the
moment of feed offer may be associated with an increase in aggression. A low level of hunger
could reduce the intensity of competition and aggression (Jensen et al., 2009; D’Eath et al.,
2011).
The commercial interest in M. rosenbergii is growing along the years, as well the
number of studies focusing on its management, and how to minimize the impact of agonistic
behavior and heterogeneous growth, characteristics which are inherent to the species. Based on
that, we intend to verify the effects of three different frequencies of feed offer on the behavior of
juvenile M. rosenbergii. We expected that behaviors related to the presence of food such as
ingestion would increase and the frequency of agonistic interactions decrease when feed is
offered more times throughout the day.
62
2. Material and methods
2.1. Experimental condition
Macrobrachium rosenbergii were obtained from a commercial hatchery while they were still in
the post-larval stage. The post-larvae were distributed in external tank nurseries. For each
experimental treatment, 28 prawns at two months old were transferred to the laboratory and
distributed in four aquariums (100 x 50 x 60 cm) with population density of 14 prawns/m². The
aquariums contained approximately 200 liters of water, sand substrate, constant aeration and a
closed system of water recirculation through biological filters. Aquariums were divided into
four quadrants (1, 2, 3 and 4) using vertical lines drawn 25 cm apart on the front surface of the
glass. An imaginary line in the middle of the aquarium separated the front and back halves of
the structure totalizing eight quadrants. The spatial position of each individual was recorded
during behavioral observations to measure its movement. Animals were housed in artificial
lighting in a 12/12 h controlled photoperiod. To control water quality, physical-chemical
parameters were monitored and maintained as follows: temperature (24.8 ± 0.8), pH (7.4 ± 0.2)
and dissolved oxygen (7.7 ± 0.8).
2.2. Experimental Procedure
After recording their weights, the prawns were allowed to acclimatize to artificial
conditions for 10 days before observations for each treatment started. Animals were submitted
to three different feeding frequency treatments: two, three and four times a day. The
experiments were not simultaneous and for each, new animals were obtained. For all treatments
observations occurred for 30 days, five days per week, four times per day at one, five, seven and
eleven hours after photoperiod transition. For the treatment in which feed offer was twice a day,
the time offer were one and seven hours after light phase transition. In the treatment where the
offer occurred three times a day, the schedules were one, seven and eleven hours after phase
63
transition. And when feed offer was four times a day, feed was available in the four hours of
observation, one, five, seven and eleven hours after the phase transition. We used commercial
granule ration with 42% of crude protein. The quantity and nutritional quality of food offered
per day did not vary between treatments.
Observations lasted 15 min per aquarium and started immediately after feed offer.
During the first five minutes agonistic behavior was recorded using the continuous focal animal
method. In the next ten minutes behavior related to the behavioral activity profile and the
position of the animal in one of the eight quadrants were observed using the instantaneous focal
animal method, with record at each minute. Food was placed in trays and removed only before
the next feeding time. Approximately after one hour of feed offer, the remnants were removed
from the tray. For all treatments the amount of food offered was equivalent to 10% of the total
biomass, partitioned according to the frequency. We recorded latency to access feeding tray and
latency to start ingestion per individual, we also recorded when an individual remained more
than thirty seconds on the tray, after feed offer.
Behaviors related to the behavioral activity profile were adapted from an ethogram of
other species of shrimp (Silva et al., 2012). The following categories were recorded: (1)
exploring the substrate, when the prawn uses pereopod chelae to investigate the substrate, the
animal may be stationary or moving; (2) pellet ingestion, the prawn uses pereopod chelae to
handle and ingest the pellet; (3) inactivity, the animal remains stationary on the substrate; (4)
burrowing, the prawn uses pereopod chelae and pleopods to remove the substrate and form a
cavity, where it remains afterwards; (5) swimming, the prawn moves horizontally or vertically
in the water column; (6) crawling, the prawn moves along the substrate; (7) auto-grooming, the
prawn uses pereopod chelae to groom the body. Exploring the substrate, swimming and
crawling are behavioral components of locomotor activity. Agonism was also recorded when
the interaction happened at the moment of sampling.
Agonistic behaviors were adapted from an ethogram that describes behaviors of M.
rosenbergii adults (Barki et al., 1991a). We recorded the following behaviors: (1) approach, one
64
prawn moves toward another; (2) move away, when one prawn moves away from another; (3)
rush, rapid movement of one prawn towards another; (4) abdomen flexing, rapid flexion of
abdomen which results in a movement upwards and backwards through the water; (5) cheliped
extension, parallel forward extension of both chelipeds towards another prawn; (6) meral
spread, an elevated body position while both chelipeds are raised horizontally with the merus
spread perpendicular to the body; (7) complete lifting, oblique lifting of both the chelipeds and
the anterior part of the body; (8) scissoring, the rapid bringing together of the two claws in a
scissoring motion on the body of another prawn; (9) embrace, one prawn surrounds another
prawn with its chelipeds; (10) push, one prawn pushes one of its chelae against the body of
another prawn; (11) chase, one prawn chases the other with their extending chelipeds.
To obtain the movement frequency of each prawn we recorded the frequency each
prawn changes the position over the period of observation. At the end of each treatment prawns
were weighted again to obtain weight gain.
2.3. Data analysis
Data were submitted to a normality test (Kolmogorov-Smirnov). According to the
result, analyzes between feeding frequencies were performed with ANOVA or Kruskal-Wallis
test, and when significant differences were found the post-hoc multiple comparisons test was
applied. Friedman test compared behaviors frequency in each feeding regime; the Wilcoxon
matched pairs test was also used when significant differences were found between them.
Significance level of p < 0.05 was adopted for all the tests.
3. Results
3.1. Feed response
To evaluate the response of prawns to feed frequency in different treatments we
compared the frequency of food ingestion, latencies for each animal to reach the feeding tray
and to start eating as well as the weight gain of animals. Feed ingestion was lower to animals
65
fed four times a day, but this result was not statistically significant (H = 1.40, d.f. = 2, P ˃ 0.05)
(Fig.1). The recorded latencies were also influenced by feed frequency. The higher latency to
reach feeding tray was observed in animals fed four times a day, prawns fed three times arrived
faster (F 2,101= 3.7682, d.f. = 2, P ˂ 0.05) (Fig.2). Animals took longer to start feeding as the
feed frequency increased (H = 6.12, d.f. = 2, P ˃ 0.05) (Fig.2). At the end of the experiment
animals gained around 1 g. The average and standard deviation of weight gain for animals at
treatments was: 1,04 g ± 0,45; 0,9 ± 0,41; 0,92 ± 0,44; respectively for feeding frequencies two,
three and four times a day. Growth was slightly higher when food was distributed in two
offerings. However this difference was not significant (F 2,80= 58567, d.f. = 2, P ˃ 0.05) (Fig.3).
In general, prawns did not remain for more than 30 s at the feeding tray. That was only observed
once in the treatments two times a day (38 s) and once at feeding frequency three times a day
(197 s).
Median
25%-75%
Min-Max 2 3 4
Feed offer
-2
0
2
4
6
8
10
12
Fe
ed
ing
estio
n
(ep
iso
de
/10
min
ute
s)
Fig.1. Frequency of feed ingestion between treatments (feed offer). No statistic difference was
observed.
66
3.2. Behavioral activity profile
Prawns were observed during the light phase of the day, given that in farms food
delivery mainly occurs at this phase; also in a previous study we did not observe difference in
feeding ingestion between light phases (Silva and Arruda, 2014). The display of behaviors can
2 3 4
Feed offer
0,5
1,0
1,5
We
igh
t Ga
in (g
)
Fig.2. Latencies to access food and to start feeding. Different letters represent statistic differences.
Fig.3.Weight gain between treatments (feed offer).
Median
25%-75%
Min-Max 2 3 4
Feed offer
0
200
400
600
800
1000
La
ten
cy to
sta
rt ea
ting
(s)
aab b
Mean
Mean±SE
Mean±SD 2 3 4
Feed offer
0
200
400
600
800
1000
La
ten
cy to
acce
ss fe
ed
ing
tray (s
)
a
b
ab
67
vary with time of day and we also expected that in presence of a stimulus such as food,
activities related to search increase. Crawling and swimming are common activities of
behavioral profile, which are associated with the movement of the animal in the environment
and can be related to the location of food. During the exploration of the substrate animal may
find, capture and handle the food before consume it. Crawling (H = 264.2880 d.f. = 2, P ˂
0.001) and swimming (H = 101.9745, d.f. = 2, P ˂ 0.001) were more frequent when animals
were fed four times a day. On the other hand exploration (H = 19.03230, d.f. = 2, P ˂ 0.05) was
lower when feeding has occurred four times a day. For all the behaviors above there was no
difference between feeding frequencies two and three times a day. Observing how many times
prawns change their position between quadrants, we obtained animals’ displacement throughout
the day. The displacement (H = 45.01733, d.f. = 2, P ˂ 0.05) was also affected by the feeding
showing a similar pattern to crawling and swimming. Animals moved more in the tank when
food was offered four times a day, and showed no difference between two and three feeding
frequencies. Inactivity (H = 29.55073, d.f. = 2, P ˂ 0.001) was lower at feeding frequency four
when compared with two times a day, but not between four and three or three and two times per
day. Auto-grooming (H = 36.29463, d.f. = 2, P ˂ 0.001) was lower at feeding frequency four,
without difference between three and two times per day. Burrowing (H = 5.965318, d.f. = 2, P ˃
0.05) was the less observed behavior and did not showed any difference between feeding
frequencies.
Analyzing the distribution of behaviors in each feeding frequency separately, significant
differences were observed when animals were fed two times (Friedman X2 (7; 1061) = 4191.540
P ˂ 0.05); three times (Friedman X2 (7; 1073) = 4037.884 P ˂ 0.05) and four times per day
(Friedman X2 (7; 1015) = 366.599, P ˂ 0.05). The results showed a similar profile for all
treatments. Auto-grooming presents the higher frequency, followed by exploration and
crawling. At feeding frequency two times a day non-significant difference was observed only
between swimming and inactivity (Wilcoxon T = 19715.0, Z = 1.06355, P ˃ 0.05); the same
68
was found at feeding frequency three times a day (Wilcoxon T = 27754.0, Z = 0.76930, P ˃
0.05).
3.3. Agonistic behavior
In our experiments prawns were observed through two different observation methods.
On the first five minutes of each window of observation, agonistic interactions were recorded
continuously, in the subsequent ten minutes were recorded instantaneously every 60 seconds.
Due to the difference in behavioral recordings data were analyzed separately. The frequency of
agonistic interactions differed between treatments in both moments, but not in the same way. In
the first five minutes of observation agonism significantly higher at feeding frequency three
times a day. Only when compared to feeding frequency four times a day (H = 7.387733, d.f. =
2, P ˂ 0.05) (Fig.4). In the next ten minutes agonism was significantly higher at feeding
frequency two times a day, when compared to four times a day (H = 52.83281, d.f. = 2, P ˂
0.05) (Fig. 5). Observing the results along the fifteen minutes, at feeding frequency four times a
day we obtained the lowest frequency of agonistic interactions, when animals fed two times a
day a tendency to higher frequency of agonism was observed.
Median
25%-75%
Min-Max 2 3 4
Feed offer
-1
0
1
2
3
4
5
6
7
8
9
Ag
on
ism (c
on
tinu
ou
s/5
min
ute
s)
a
ab
b
Fig.4. Frequency of agonistic interactions in the first five minutes of observation,
compared between feed offer.
69
4. Discussion
When assessing the frequency of food ingestion and weight gain, the response of
animals did not show great differences between feeding frequencies. Ingestion was slightly
lower at feeding frequency four times a day which resulted in lower weight gain at this
treatment. Our first hypothesis, therefore, was not confirmed. Litopenaeus vannamei fed three,
four or seven times a day presents higher feeding ingestion when fed three times, the weight
gain did not differ between three and four times, but decreased at seven feeding frequency
(Pontes et al., 2008). When shrimps of species Penaeus monodon were fed three, four, five and
six times no effect were observed on growth rate (Smith et al., 2002).
We observed that as the food is offered more times along the day, the intensity of
animal’s response tends to decrease. Animals took longer to respond to food at feeding
frequency four times a day. Latencies to reach the feeding tray and consume the ration were
higher at this feeding frequency. Motivation to feed can be assessed by some factors as latency
to start feeding, time spent feeding and frequency of feed intake (Martins et al., 2011). M.
rosenbergii showed higher motivation to feed when food was offered only two times a day.
When fed three times the time to achieve the tray was shorter when compared to those fed
Median
25%-75%
Min-Max 2 3 4
Feed offer
0
2
4
6
8
Agonis
m (epis
odes/1
0 m
inute
s)
a
ab b
Fig.5. Frequency of agonistic interactions in the last ten minutes of observation, compared between
feed offer.
70
twice, however the time until the initial intake was longer. Animals that did not have the
opportunity to display a particular behavior, due to the absence of a stimulus, may present an
increase in the behavior frequency when the stimulus reappears (Dawkins, 1990).
Auto-grooming was the most exhibited behavior in all feeding frequencies, but when
compared between treatments prawns fed four times a day displayed less this behavior.
Crawling was also a predominant behavior in the three treatments. Its frequency was higher at
feeding four times a day, the same was observed to swimming and displacement. Prawn’s
displacement in the aquarium results from behaviors related to individual’s locomotion such as
crawling and swimming. So the similarity between the data was expected. The exploratory
behavior was last frequent at feeding frequency four times a day as food ingestion were.
Exploration of environment is an important component of animal’s daily activity, during
exploration prawns uses its pereopods and claws to scavenging the substrate, and when it
encounters an item the animal can manipulate or discard it. In the marine shrimps L. vannamei
and Farfantepenaeus subtilis exploratory behavior increased when food was offered, this
reinforces the association of this behavior with food acquisition (Pontes et. al., 2006; Lima et.
al., 2009; Silva et. al., 2012). Prawns spent more time inactive when fed two or three times a
day. As emphasized above, crawling and swimming, prawn’s displacement and also but to a
lesser extent substrate exploration are behaviors associated with locomotion. On the other hand,
during behaviors such as auto-grooming and inactivity, prawns remain stationary i.e. without
moving around the aquarium. So when food was available four times a day M. rosenbergii tends
to spend more time in locomotor activities, which may also result in a higher energy
expenditure.
To perform an activity the animal uses time and energy, which cannot be allocated to
different activities simultaneously. If this activity does not involve feeding the individual needs
to have energy reserves (Cuthill and Houston, 1997). In this way analyzes of a species daily
feeding pattern have to take into account the distribution pattern of other behaviors. When
feeding distribution is modified, time and energy invested in others behavior also changes. An
71
efficient feeding management system should take into consideration the animal’s expression of
all behaviors (Pontes et. al., 2008).
The partitioning of food in two, three or four times a day influenced agonistic behavior.
In the first five minutes after feed offer agonistic interactions were more frequent when feed
was delivered three times; the other two treatments produced similar results. However,
observing the subsequent ten minutes, the more partitioned feed offer the lower the frequency of
agonistic interactions. Based on latency and ingestion data, motivation to feed decreases as feed
frequency increases. In a contest for food animal’s motivational state is an important factor
influencing the investment on fight. Even if one contestant has the potential to win and hold the
resource it can choose not to, the resource involved may not be so valuable at that moment
(Laidre and Elwood, 2008).
Individuals competing for a resource often differ in their competitive ability which
could lead to differences in success. Food distribution in time and space can influence the
intensity of interference competition and its results (Hakoyama and Iguchi, 1997). M.
rosenbergii juveniles submitted to three different feeding frequencies did not present variation
in feed ingestion and weight gain. However agonistic interactions decrease when feed was
offered four times a day. The way species respond to manipulations of feeding conditions will
depend of the predictability of food they were adapted to (Roger, 1993; Roger et. al., 1994).
Studies which investigated feeding management in shrimps and prawns has presented different
results, but there is a consensus about the importance of the differences on the behavior between
species, once those differences could have an impact in the success of the husbandry system.
Acknowledgements
We would like to thank the Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), the Coordenação de Aperfeiçoamento de Pessoal de Nível superior
(CAPES) and the Department of Physiology of the Universidade Federal do Rio Grande do
Norte for their support in developing this study.
72
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Dawkins, M.S., 1990. From an animal’s point of view: motivation, fitness, and animal welfare.
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Duarte, C., Jaramillo, E., Contreras, H., Acuña, H., 2010. Cannibalism and food availability in
the talitrid amphipod Orchestoidea tuberculata. J. Sea Res. 64, 417-421.
Goldeberg, J.L., Grant, J.W.A., Lefebvre, L., 2001. Effects of the temporal predictability and
spatial clumping of food on the intensity of competitive aggression in Zenaida dove. Behav.
Ecol. 12, 490-495.
Hakoyama, H., Kei'ichiroh, I.,1997. Why is competition more intense if food is supplied more
slowly? Behav. Ecol. Sociobiol. 40, 159-168.
Jensen, M. B., Pedersen, L. J., Theil, P. K., Yde, C. C., Bach Knudsen, K. E., 2009. Feeding
motivation and plasma metabolites in pregnant sows fed diets rich in dietary fiber either once or
twice daily. J. Anim. Sci. 90, 1910-1919.
Karplus, I., Hulata, G., Zafrir, S., 1992. Social control of growth in Macrobrachium
rosenbergii. IV. The mechanism of growth suppression in runts. Aquacult. 106, 275-283.
73
Karplus, I., 2005. Social control of growth in Macrobrachium rosenbergii (De Man): a review
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Laidre, M.E., Elwood, R.W., 2008. Motivation matters: cheliped extension displays in the
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Lima, P.P., Pontes, C.S., Arruda, M.F., 2009. Activity pattern of the marine shrimp Litopenaeus
vannamei (Boone 1931) in laboratory as a function of different feeding frequencies. Aquacult.
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Martins, C. I.M., Conceição, L.E.C., Schrama, J.W., 2011. Consistency of individual variation
in feeding behaviour and its relationship with performance traits in Nile tilapia Oreochromis
niloticus. Applied Anim. Behav. Sci. 133, 109–116.
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75
8. DISCUSSÃO GERAL
Neste trabalho investigamos o comportamento de juvenis da espécie de camarão
de água doce Macrobrachium rosenbergii, submetidos a condições semelhantes à de
viveiro. Esta espécie tem sido cultivada em diversos países o que tem incentivado o
desenvolvimento de pesquisas sobre sua fisiologia, comportamento, bem como sobre o
aprimoramento das técnicas de manejo deste camarão em viveiros. É inegável o
potencial de M. rosenbergii para a carcinicultura, entretanto características da espécie
exigem estratégias apropriadas para garantir o sucesso da produção. Usando o estudo do
comportamento animal como ferramenta, buscamos contribuir para o desenvolvimento
destas estratégias. Para isso investimos no conhecimento sobre o perfil comportamental
de M. rosenbergii juvenis e na caracterização da sua resposta comportamental a
manipulações relacionadas ao alimento e abrigo, recursos valiosos para espécie.
Dentre as principais características de M. rosenbergii consideradas limitantes
para o cultivo estão o comportamento agonístico e crescimento heterogêneo (Karplus,
2005). Estas características são observadas em todas as fases do desenvolvimento do
animal. Machos adultos apresentam três morfotipos que diferem na sua morfologia,
fisiologia e comportamentos. Entre eles há uma hierarquia de dominância onde o macho
de quela azul domina o macho de quela laranja, o qual domina o macho de quela
pequena. Em fêmeas estas diferenças e relações não são observadas. Juvenis já
apresentam diferença no tamanho corporal, alguns indivíduos crescem mais e
rapidamente os quais são chamados saltadores e outros apresentam crescimento mais
lento, são chamados de retardatários (Ra’anan & Cohen 1984, Karplus, Hulata,
Wohlfarth & Halevy, 1987). Poucos dados discutem como esta diferença, na fase de
juvenil, pode influenciar o comportamento dos animais e as relações entre eles.
76
É sabido que mecanismos sociais tem sido considerados como principais
reguladores do crescimento em M. rosenbergii e consequentemente da heterogeneidade
observada. São eles: competição direta, supressão do apetite, alteração na eficiência de
conversão do alimento e altos níveis de atividade locomotora (Karplus, 2005).
Investigamos o efeito de alguns destes mecanismos em grupos de quatro indivíduos
distribuídos num ranque de dominância. Os resultados mostraram que não houve uma
correlação entre a posição no animal no ranque de dominância com a frequência de
ingestão do alimento, embora juvenis dominantes tenham chegado com mais frequência
à bandeja de alimentação e obtiveram maior ganho de peso ao final do experimento.
Indivíduos subordinados não apresentaram maiores níveis de atividade locomotora.
Apesar de não termos realizado nenhuma medida neste sentido, nossos dados
corroboram o mecanismo de alteração na eficiência de conversão como principal
responsável pela heterogeneidade no crescimento dos animais (Karplus et al., 1992).
O perfil de atividades comportamental de M. rosenbergii é semelhante ao
exibido por outras espécies de crustáceos (Pontes, 2006; Silva et al., 2012). Os
comportamentos de limpeza e exploração são bastante frequentes, seguidos por natação,
rastejamento, parado e alimentação. O comportamento cavar foi pouco observado em
todos os experimentos. Quando comparamos a frequência dos comportamentos entre as
fases de claro e escuro do ciclo de 24 h, não identificamos um padrão
atividade/inatividade entre elas. Todos os comportamentos foram exibidos nas duas
fases com algumas variações. Em muitas espécies, juvenis e adultos diferem na
distribuição das atividades, animais adultos tendem a exibir maiores períodos de
inatividade, enquanto juvenis tendem a ser mais ativos. Além da idade fatores
ambientais também influenciam a distribuição dos comportamentos (Kenyon,
Loneragan & Hughes, 1995).
77
Na segunda etapa do nosso estudo observamos o comportamento dos camarões
associados a dois diferentes tipos de abrigo. Esperávamos que com abrigo disponível o
animal passasse a maior parte da fase de claro entocado. Nossos resultados mostraram
que não só a fase do ciclo de luz, mas também o tipo de abrigo influenciaram nesta
reposta. Apenas camarões associados ao abrigo de tela exibiram uma maior frequência
de permanência na fase de claro. Camarões nos aquários com tijolo permaneceram mais
no abrigo na fase de escuro. O tipo de abrigo foi um fator de grande influência no
comportamento dos camarões, provavelmente devido as características estruturais dos
materiais escolhidos. Apesar de não termos investigado a preferência dos animais pelo
tipo de abrigo, observamos uma maior frequência de uso do abrigo de tijolo. Além
disso, o tijolo levou a uma diminuição na frequência das interações agonísticas. Este
resultado se deve a estrutura do tijolo que fornece uma barreira mais eficiente para a
disseminação de pistas químicas, visuais e até tácteis que informam o indivíduo da
presença do coespecífico (Cenni, Parisi & Gherardi, 2010).
Para que um indivíduo alcance o sucesso reprodutivo ele deve investir na
aquisição de recursos. Em muitas espécies os animais competem pelo acesso a esses
recursos. Essa competição pode envolver comportamentos agressivos e o
estabelecimento de uma hierarquia de dominância, onde o dominante teria vantagem no
acesso ao recurso. Quando classificamos os juvenis nesse segundo experimento numa
hierarquia de dominância e correlacionamos a frequência de uso do abrigo com sua
posição no ranque, não identificamos uma correlação significativa. Diferente da etapa I
onde o dominante alcançou com maior frequência a bandeja de alimentação, não
observamos uma vantagem no acesso ao abrigo dos indivíduos nos postos mais altos da
hierarquia.
78
Além da habilidade competitiva e status de dominância, a distribuição do
recurso no ambiente também interfere no sucesso do indivíduo (Bryant & Grant, 1995;
Goldeberg, Grant & Lefebvre, 2001). Quando ofertamos a mesma quantidade de
alimento em frequências diferentes ao longo do dia, a resposta dos camarões ao
alimento foi alterada. Ao contrário do que era esperado, camarões alimentados quatro
vezes ao dia apresentaram uma redução na frequência de ingestão. A latência para
chegar ao alimento e consumi-lo foi maior nesse tratamento. Frequência de ingestão,
tempo se alimentando e tempo para iniciar a alimentação são medidas para a motivação
do animal com relação ao alimento (Martins, Conceição & Schrama, 2011). Assim,
camarões alimentados quatro vezes ao dia estão menos motivados para buscar o
alimento. Esta diminuição na motivação para alimentação pode ter influenciado o
resultado do comportamento agonístico. Camarões alimentados quatro vezes ao dia
exibiram uma frequência mais baixa de interações agonísticas. O quanto o indivíduo
investe num confronto por um recurso depende também da motivação do animal para
adquirir esse recurso (Laidre & Elwood, 2008).
Como dito anteriormente, o comportamento agressivo de M. rosenbergii tem
sido apontado como um dos principais fatores limitantes ao sucesso do seu cultivo.
Nossos resultados mostraram que medidas simples de manejo, baseadas o
comportamento da espécie podem diminuir o impacto do agonismo e consequentemente
melhorar a sobrevivência e a qualidade dos camarões obtidos ao final da produção. Na
tabela abaixo encontra-se de forma resumida os resultados e conclusões obtidos para as
nossas hipóteses.
79
Quadro:.hipóteses e resultados obtidos.
HIPÓTESE 1: Há diferenças no acesso ao alimento e no crescimento entre indivíduos dominantes
e subordinados
PREDIÇÕES RESULTADOS CONCLUSÃO
Predição 1: dominantes
apresentarão maior frequência
de chegada à bandeja, de
ingestão do alimento e maior
ganho de peso.
Não foi observada correlação entre
a frequência de ingestão do
alimento e a posição no ranque de
dominância. Entretanto dominantes
chegaram mais vezes à bandeja de
alimentação e tiveram maior ganho
de peso.
Parcialmente corroborada
Predição 2: a latência de
chegada à bandeja e de
consumo do alimento será
menor para os dominantes.
Não houve diferença entre
dominantes e subordinados com
relação às latências na resposta ao
alimento
Não corroborada
Predição 3: indivíduos
subordinados exibirão
frequências mais altas de
atividades associadas a
locomoção, como natação,
rastejamento e exploração
Não foi observada correlação entre
os níveis de atividade locomotora e
a posição dos indivíduos no ranque
de dominância.
Não corroborada
HIPÓTESE 2: Como as demais espécies de crustáceos, M. rosenbergii apresenta diferenças no
perfil de atividades entre as fases de claro e de escuro do ciclo de 24 horas.
PREDIÇÕES RESULTADOS CONCLUSÃO
Predição 1: atividades
relacionadas à locomoção são
mais frequentes na fase de
escuro.
A exploração foi mais frequente na
fase de claro. Rastejamento,
natação e parado foram mais
frequentes na fase de escuro. Não
foi identificado um padrão
atividade/inatividade entre as fases
do ciclo.
Não corroborada
80
Predição 2: as interações
agonísticas são mais intensas
na fase de escuro, já que os
comportamentos de
ritualização/avaliação seriam
pouco eficientes nesta fase.
Comportamentos indicadores de
um alto nível de agressividade,
como atacar e flexão abdominal,
foram mais frequentes na fase de
escuro.
Corroborada
Predição 3: os animais
permanecem inativos na fase
de claro; havendo
disponibilidade de abrigo, M.
rosenbergii passará a maior
parte da fase de claro nesses
locais.
Apenas quando o abrigo disponível
era a tela, este padrão foi
observado. No abrigo de tijolo a
frequência de permanência foi mais
alta na fase de escuro.
Parcialmente corroborada
HIPÓTESE 3: o tipo do abrigo (tijolo ou rolo feito com tela) interfere no seu uso pelo animal e no
comportamento de Macrobrachium rosenbergii.
PREDIÇÕES RESULTADOS CONCLUSÃO
Predição 1: a frequência de
permanência no abrigo será
mais alta quando os camarões
estiverem associados ao abrigo
de tijolo, uma vez que as
características deste material
(coloração escura, barreira entre
as câmaras) são mais atrativas
para os animais.
A frequência de permanência no
abrigo foi mais elevada quando o
abrigo disponível era tijolo.
Corroborada
Predição 2: a frequência de
interações agonísticas será mais
baixa no abrigo de tijolo
quando comparado ao abrigo de
tela.
As interações agonísticas forma
mais frequentes quando os
camarões estavam associados ao
abrigo de tela.
Corroborada
81
HIPÓTESE 4: a oferta do alimento modifica a expressão dos comportamentos em Macrobrachium
rosenbergii.
PREDIÇÕES RESULTADOS CONCLUSÃO
Predição 1: considerando o
limite fisiológico da espécie,
espera-se que quanto maior a
frequência de oferta alimentar,
maior a frequência de ingestão
desse alimento.
Camarões alimentados quatro
vezes ao dia apresentaram a
menor frequência de ingestão do
alimento.
Não corroborada
Predição 2: comportamentos
relacionados à busca e captura
do alimento serão mais
frequentes nos horários em que
o alimento for ofertado.
Natação e rastejamento,
comportamentos relacionados a
busca do alimento, foram mais
frequentes quando os animais
foram alimentados quatro vezes
ao dia. Entretanto a exploração
foi menos frequente neste
tratamento.
Parcialmente corroborada
Predição 3: as interações
agonísticas devem diminuir à
medida que a oferta do alimento
for mais frequente, já que
alguns indivíduos vão se saciar
nas primeiras ofertas e não
competirão pelo recurso nas
demais.
Camarões alimentados quatro
vezes ao dia apresentaram a
menor frequência de interações
agonísticas.
Corroborada
82
Nesse estudo vimos que o tipo do recurso, sua qualidade e como ele está
distribuído no ambiente afetam o comportamento animal. Além disso, as diferenças
individuais podem ser relevantes nas respostas observadas. O conhecimento desses
aspectos permite ao pesquisador e ao produtor desenvolver estratégias de manejo
adequadas. Neste sentido o comportamento animal tem sido utilizado como importante
ferramenta no manejo de diversas espécies. Através da abordagem comportamental é
possível alcançar uma condição de bom bem-estar para os animais, garantindo seu
desenvolvimento saudável, o que contribui para a sustentabilidade da atividade e
beneficia a produção animal.
83
9. CONCLUSÃO
- Macrobrachium rosenbergii, na fase de juvenil, apresenta hierarquia de dominância a
qual beneficia os dominantes para o acesso ao alimento. No entanto, quando o alimento
ofertado era abundante a frequência de ingestão não diferiu entre os indivíduos.
- A hierarquia de dominância não influenciou o uso do abrigo. Todos os indivíduos,
independente da sua posição no ranque de dominância, utilizaram o abrigo com
frequência semelhante.
- Juvenis são ativos nas duas fases do ciclo de luz. Entretanto na presença do abrigo de
tela, os animais utilizaram mais o abrigo na fase de claro.
- A presença do abrigo de tijolo e a oferta do alimento numa frequência maior ao longo
do dia, diminuíram a frequência das interações agonísticas.
84
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