Evaluation of behavioral changes induced by a first step of domestication or selection for growth in the European sea bass (Dicentrarchus labrax): A self-feeding approach under repeated acute stress
Introduction
Fish domestication can be defined as “the process by which a population of animals becomes adapted to humans and to the captive environment by some combination of genetic changes occurring over generations and environmentally induced developmental events re-occurring during each generation” (Price, 1984). Selection is usually used to improve traits strongly associated to production cost (e.g. growth rate, disease resistance, age at maturity, flesh quality), but very little is known on selected fish capacities to tolerate stress per se. It was nevertheless shown that fish responsiveness to stress has a genetic component that could be, therefore, modified by selective breeding (Pottinger and Pickering, 1997). Indeed, Pottinger and Pickering, 1997, Pottinger and Carrick, 1999 have shown that it was possible to select rainbow trout (Oncoryhnchus mykiss, Walbaum) strains presenting a high or low cortisol response to confinement stress. These strains have also shown other clear behavioral and physiological differences such as a quicker resumption of feeding, when placed in a novel environment, for the low cortisol responding strain (Overli et al., 2004, Overli et al., 2002), and a lower brain serotonin concentration (Overli et al., 2005). According to these results, it seems feasible to generate strains displaying a high stress tolerance, and thus, improved performances in aquaculture, across a number of traits (e.g. improvement of feed conversion efficiency, growth, fecundity, egg quality, post-slaughter flesh quality and also reduction in the incidence of disease), and in addition an improvement of their welfare (Pottinger and Pickering, 1997).
The sea bass (Dicentrarchus labrax, L.) is an important species in Mediterranean and Atlantic aquaculture that was recently domesticated. Therefore, very little is known on effects of the very early step of domestication or selection for growth apart from classical traits of commercial interest (Dupont-Nivet et al., 2008, Vandeputte et al., 2009) and specially nothing is know, on behavioral responses to stress exposure and welfare potential. Though, stress is an unavoidable component of finfish aquaculture environment (Pottinger and Pickering 1997), and is also largely associated to fish welfare, which is an important issue for the industry, not just for public perception, marketing and production acceptance, but also often in terms of production efficiency, quality and quantity (Bull et al., 1996, Southgate and Wall, 2001, Huntingford et al., 2006). Therefore, even if stress responses do not highlight all welfare disturbances, it is generally admitted that they strongly indicate a poor welfare (Bull et al., 1996, Huntingford et al., 2006). Such evidences led to an active research on potential methods to reduce stress responses in aquaculture species (Ashley, 2007). Among them, domestication and selective breeding to minimize fish responsiveness to stressors, was a major axis of research of the last few years (Pottinger, 2003).
The present study thus proposes to evaluate the early effect (one generation) of fish domestication and selection for growth on behavior changes. The chosen approach was an evaluation of the modifications induced in self-feeding (feed demand rhythm, quantities of food intake and wasted) by repeated acute stress exposure (stress tolerance used as a screening procedure). Growth performance (body mass, body condition factor, specific growth rate) was recorded as complementary traits.
Section snippets
Experimental set up
The four populations from where the fish tested in this experiment were sampled, were produce to evaluate the response to selection for growth in the frame of a genetic EU project (Competus COOP-CT-2005-017633) and the details of rearing conditions and sizes of these populations can be found in Vandeputte et al., 2009. In summary, the four tested populations have been hatched and reared at the experimental research station of Ifremer in Palavas-les-Flots (France). Until the start of the
Results
During the experiment, some fish died for different reasons i.e. some jumped out of the tank or for unidentified causes, however, no mortality could be allocated to stress or anesthesia: it concerned 1 Wild fish during P1, 1 Wild and 1 Domesticated fish during P3; 2 Domesticated and 2 Selected A fish during P4. These changes in the number of individuals were taken into account in all measured variables.
Discussion
At the beginning of the experiment fish were naive facing the self-feeder and whatever the group they really began to correctly activate it after 14 days. This period was thus synonym of food deprivation and as a consequence, characterized by a loss of fish body mass, a negative growth rate and a decrease of K factor for all populations. The loss of body mass during this period was comparable between Selected A, B and Wild groups indicating an analogous metabolic utilization that was higher than
Conclusion
The results of this study, pointed out that the improvement of growth performance induced by a first generation of domestication or selection for growth in sea bass was mainly due to a higher appetite rather than a better feed efficiency but that, at this early stage, behavioral responses to repeated acute stress were not modified. Finally, to better evaluate the effects of domestication or selection processes, it will be useful to investigate, in future experiments, the effect of additional
Acknowledgements
This work was performed within the Integrated Research Project SEAFOODplus, contract no. FOOD-CT-2004-506359 and the STREP Project FASTFISH, contract no. 022720. It is part of the program of the GDR Agπ, INRA-Ifremer research group for sustainable fish breeding. The financing of this work by the European Union and by the county council of Charente Maritime is gratefully acknowledged. This study was conducted under the approval of the Animal Care Committee of France under the official licence of
S. Millot, PhD in Oceanography from Ifremer and University of La Rochelle, France. Master degree in Biology of Behaviour from the University of Paris XIII, France.
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Cited by (0)
S. Millot, PhD in Oceanography from Ifremer and University of La Rochelle, France. Master degree in Biology of Behaviour from the University of Paris XIII, France.
S. Péan, second-year Ph.D. Student in Oceanography from Ifremer and University of La Rochelle, France. Master degree in Coastal Ecology from the University of La Rochelle, France.
D. Leguay, engineer at Ifremer, with specialities in design, realization and development of scientific tools in the fields of ecotoxicology, physiology and fish welfare.
A. Vergnet, engineer at Ifremer, with specialities in design, realization and development of scientific tools in the fields of in aquaculture of marine fishes.
Béatrice Chatain, PhD, is a senior scientist in aquaculture of marine fishes, with specialities in larval zootechny and genetics. She has coordinated 4 EU research projects in the field of sea bass genetics.
Marie-Laure Bégout, PhD, is a senior scientist studying biological basis of behavioral adaptation and analysing underlying physiological mechanisms. She has participated in several Welfare EU projects.