Genotype by diet interactions in European sea bass (Dicentrarchus labrax, L.) in case of a nutritional challenge on totally plant-based diets 1

Aquaculture of carnivorous species has strongly relied on fish meal and fish oil for feed formulation and higher and higher replacement by terrestrial plant-based products is occurring now. This rapid change in dietary environment has been a major evolution and has to be taken into consideration in breeding programs. The present study analyzed potential consequences of this tendency for selective breeding, by estimating genetic parameters of body weight and growth rates estimated by TGC (Thermal Growth Coefficient) over different periods with extremely contrasted diets. European sea bass (Dicentrarchus labrax L.) issued from a factorial cross (1,526 fish) between 25 sires and 9 dams were used to estimate heritabilities and genotype by diet interaction. Starting 87 days after fertilization (2.5 g), half of them were fed a diet containing marine products (M) and the other half was fed a totally plant-based (PB) diet (without any fishmeal and any fish oil). They were individually tagged, reared in a recirculated system and genotyped at13 microsatellites to rebuild parentage of individuals. Body weight and TGC were measured during 335 days until fish fed M diet reached 108.3 g. These traits were significantly lower in fish fed the PB diet (P 0.1). Survival was significantly lower in fish fed the PB diet (PB: 64.7% M: 93.7% after 418 days, P<0.05). This work evidenced moderate heritabilities (0.18 to 0.46) for body weight (BW) with both diets and high genetic correlations between diets (0.78 to 0.93) meaning low genotype by diet interactions, although diets were extremely contrasted. Heritabilities of TGC (0.11 to 0.3) were lower than for BW as well as genetic correlations between diets (0.43 to 0.64). Using such extremely contrasted diets, predicted gains in different scenarii indicated that selecting fish for growth on a marine diet should be the most efficient way to increase growth on plant-based diets, meaning that in this case indirect selection should be more efficient than direct selection.