Génétique de l'utilisation des produits d'origine végétale chez la truite arc-en-ciel (Oncorhynchus mykiss) et le bar européen (Dicentrarchus labrax)

Abstract : Nowadays, aquaculture contributes to half of the aquatic products intended for human consumption. The composition of aquafeeds strongly evolved in the past 30 years. Terrestrial plant-based products gradually replace fish meal and fish oil, as fish stocks used for their production reach their exploitation limit. However, the use of diets containing vegetable oils and meals only still lead to growth and health degradation in salmonids and marine fish.Besides, breeding programmes in fish farming allowed strong genetic progress, since 1980, on growth, health and quality traits. An important issue for fish breeders is now to understand the consequences of this deep dietary change on the current and future selected populations and to adapt breeding programs accordingly.Focusing on the comparison between two experimental diets, a diet containing marine products (M) and a diet containing only plant-based products, (PB), we investigated the possible impact of the dietary changes on the organization and the objectives of breeding programs in two major species of the French sector: the European sea bass (Dicentrarchus labrax) and the rainbow trout (Oncorhynchus mykiss). A key objective was to estimate the heritabilities of the main traits of economic interest and the importance of genotype by diet interactions, which may cause genotypes rerankings according to diet used. We also sought the potential origin of the variability for ability to use the PB diet and proposed scenarii for evolution of breeding programs.The trials confirmed that substitution of marine ingredients by vegetal ones decreased growth and lipid composition in both species, as well as survival in sea bass and, to a lesser extent in rainbow trout. The estimates of heritabilities for weight, growth and processing traits (carcass viscera, head and filet yields only measured on trout) when fish were fed with the PB diet were high in rainbow trout (respectively 0.69; 0.65; 0.21-0.58) and weak in sea bass (respectively 0.18 and 0.11). In trout and sea bass, these estimates were respectively higher and lower than those obtained when fish were fed the M diet. For these traits, genotype by diet interactions were moderate and the genetic correlations between the M and PB diets were variable in trout (respectively 0.67-0.90; 0.92; 0.65-0.96) and sea bass (respectively 0.51-0.96; 0.64) but could involve important family rerankings according to the period of survey. According to heritability estimates, expected genetic gains would be higher in trout for fish fed the PB diet than for fish fed the M diet when they would be weaker in sea bass. In trout, the measurement of the response to one generation of selection for the ability to grow and survive when fed the PB diet confirmed the results, and provided high genetic gains for body weight (+35%), survival rate (+15,1%) and produced biomass (+ 54,4%) without any impact on the processing traits (carcass, viscera, head, filet). We showed that this ability was associated to modifications in the lipid metabolism activities but could not establish links with feed intake or feed efficiency from our trials. Higher mortality rate and lower body weight in the PB batches during the first days following distribution of PB diet as well as stronger family rerankings in early steps of the survey indicate than the early stages play a key role in the use of plant-based diet at both phenotypic and genetic levels. Further insights dedicated to these particular stages are strongly needed.Based on present results, it seems possible to exploit the great plasticity of some fish species to conceive breeding programs taking into account a changing dietary environment. Facing the world limitation in food resources, genetic improvement of fish livestock can be a useful lever to facilitate dietary transitions.
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Richard Le Boucher. Génétique de l'utilisation des produits d'origine végétale chez la truite arc-en-ciel (Oncorhynchus mykiss) et le bar européen (Dicentrarchus labrax). Génétique animale. AgroParisTech, 2011. Français. ⟨NNT : 2011AGPT0064⟩. ⟨pastel-00808583⟩

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