AGONISTIC BEHAVIOUR OF JUVENILE WHITE SEABREAM (Diplodus sargus): IMPLICATIONS FOR AQUACULTURE ANA SOFIA RIBEIRO GONÇALVES Tese de doutoramento em Ciência Animal 2012 ANA SOFIA RIBEIRO GONÇALVES AGONISTIC BEHAVIOUR OF JUVENILE WHITE SEABREAM (Diplodus sargus): IMPLICATIONS FOR AQUACULTURE Tese de Candidatura ao grau de Doutor em Ciência Animal, Especialidade em Sistemas de Produção, submetida ao Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto. Orientador – Doutor Vitor Carvalho Almada Professor Catedrático Instituto Superior de Psicologia Aplicada. Co-orientador – Doutora Liliana de Sousa Professor Associado Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto. Esta tese foi financiada pela Fundação para a Ciência e Tecnologia através de uma bolsa de doutoramento com a referência SFRH/BD/42226/2007 Agradecimentos Em primeiro lugar agradeço aos meus orientadores por todo o conhecimento que me transmitiram no decorrer do trabalho, pelas sugestões e críticas que amadureceram o trabalho e me ajudaram a crescer. Agradeço aos colegas por todas as leituras, sugestões e comentários. Obrigada também por toda a ajuda no mar. À minha família pelo apoio constante e pela paciência com que me ouviram falar de um tema que lhes era estranho. Aos amigos com quem partilhei algumas dúvidas e me devolveram bons conselhos. Contents Page List of publications ............................................................................................................. i Abstract ............................................................................................................................. iii Resumo ............................................................................................................................... v Chapter 1. General introduction ....................................................................................... 1 The importance of behavioural studies ............................................................................ 3 Ethology – a discipline with multiple applications ......................................................... 3 Ethology in clinical and biomedical sciences ................................................................ 3 Ethology in production systems ................................................................................... 5 Aggression: scenarios and patterns ................................................................................. 7 Conflicts of interest – contexts, features and consequences ....................................... 7 Types of aggressive interactions .................................................................................. 7 Agonistic behaviour – definition and behaviour patterns .............................................. 8 Dominance hierarchies ........................................................................................... 9 Territoriality ............................................................................................................ 11 Common features of fish agonistic interactions .......................................................... 12 Effects of aggression on growth ..................................................................................... 13 White seabream as a case study .................................................................................. 14 Biology and ecology of Diplodus sargus ................................................................... 14 Earlier studies on aggression, growth and welfare of Diplodus sargus ...................... 15 Dominance hierarchies and growth ........................................................................... 16 Interspecific interactions and growth ......................................................................... 17 Natural habitats: what happens? ............................................................................... 17 Movements in the intertidal ....................................................................................... 18 Aims of the present study ........................................................................................... 19 References ................................................................................................................. 21 Chapter 2. Dominance and growth of Diplodus sargus (Pisces: Sparidae) in small captive groups ............................................................................................... 31 Chapter 3. Agonistic behaviour and growth of white seabream Diplodus sargus L. 1758 living in monospecific and mixed groups ......................................... 45 Chapter 4. Agonistic behaviour and shoal composition of juvenile Diplodus sargus in natural habitats: first field observations ................................................ 57 Chapter 5. When to dine? Tidal migrations and feeding activity of white seabream Diplodus sargus juveniles ............................................................................ 71 Chapter 6. General discussion ....................................................................................... 79 Dominance hierarchies and growth ........................................................................... 81 Interspecific interactions and growth ......................................................................... 83 Natural habitats: what happens? ............................................................................... 84 Movements in the intertidal ....................................................................................... 85 General considerations ............................................................................................. 86 References ................................................................................................................. 89 ............................................................................................................................................... List of publications Gonçalves A.R., de Sousa L., Coelho P.D., Almada V.C. When to dine? Tidal migrations and feeding activity of white seabream Diplodus sargus juveniles. Submitted to Marine Biology Research. Gonçalves A.R., F.S. Matheus, Vendrell C.L., Almada V.C. Agonistic behaviour and shoal composition of juvenile Diplodus sargus in natural habitats: first field observations. Submitted to Marine Biology Research. Gonçalves A.R., de Sousa L., Almada V.C. Agonistic behaviour and growth of white seabream Diplodus sargus L. 1758 living in monospecific and mixed groups. Submitted to Journal of Fish Biology. Gonçalves A.R., de Sousa L.C., Almada V.C. 2012. Dominance and growth of Diplodus sargus (Pisces: Sparidae) in small captive groups. Applied Animal Behaviour Science 137: 96-100. i ii Abstract The white seabream Diplodus sargus is an economically relevant sparid species in southern European countries. Although several attempts have been made to introduce the species in aquaculture, the slow growth recorded in captivity after the first year of life makes the aquaculture of D. sargus unprofitable. It has been suggested that this decrease of growth is related to the high levels of aggression displaced by D. sargus in captivity. In this view, we proposed to study several aspects of growth and aggression in groups of Diplodus sargus. In the present work, a detailed analysis of the structure of dominance orders in captive groups of D. sargus was provided and the growth rate of each individual in the group was assessed. Specifically, we tested the hypothesis that, if stable dominance orders were established, dominant fish would grow faster and show better condition factors than losers at the end of the experiment. The predominance of linear structures and the level of stability from week to week were revealed. No significant correlation was found between the dominance index with either growth rate or final condition factor. Thus, in relatively short time windows, aggressive behaviour seems not to be a major cause of unequal growth. We compared the growth and agonistic behaviour of D. sargus between monospecific groups and groups where white seabream were reared together with golden grey mullet, Liza aurata. The hypothesis that the presence of golden grey mullet would reduce intraspecific aggression between D. sargus and improve their growth was contradicted. The lack of improvement in growth may be explained either by efficient competition for food by golden grey mullet or by an increased expenditure of energy and/or les time to feed in contexts of higher levels of aggression. The results showed that the pattern of intraspecific interactions changed in the presence of one different species without benefits to D. sargus which argues in favor of behavioural studies when selecting species for mixed cultures. In spite of the considerable literature on aggression of white seabream in artificial conditions, there were no data available on aggression of D. sargus in natural situations. We conducted behavioural observations of juvenile Diplodus sargus in natural habitats to test whether agonistic interactions occur in natural circumstances and, if they do, in which context they happen. The first data on the agonistic behaviour of D. sargus in natural habitats demonstrate unequivocally that agonistic behaviour is an integral part of the natural behaviour of juvenile Diplodus sargus. Nevertheless, a high discrepancy in the frequency of agonistic interactions was found between natural habitats and captivity where the magnitude and