No abstract

Polygenic sex determination, although suspected in several species, is thought to be evolutionarily unstable and has been proven in very few cases. In the European sea bass, temperature is known to influence the sex ratio. We set up a factorial mating, producing 5.893 individuals from 253 full-sib families, all reared in a single batch to avoid any between-families environmental effects. The proportion of females in the offspring was 18.3%, with a large variation between families. Interpreting sex as a threshold trait, the heritability estimate was 0.62 6 0.12. The observed distribution of family sex ratios was in accordance with a polygenic model or with a four-sex-factors system with environmental variance and could not be explained by any genetic model without environmental variance. We showed that there was a positive genetic correlation between weight and sex (r A ¼ 0.50 6 0.09), apart from the phenotypic sex dimorphism in favor of females. This supports the hypothesis that a minimum size is required for sea bass juveniles to differentiate as females. An evolution of sex ratio by frequency-dependent selection is expected during the domestication process of Dicentrarchus labrax populations, raising concern about the release of such fish in the wild.

BackgroundEfforts towards utilisation of diets without fish meal (FM) or fish oil (FO) in finfish aquaculture have been being made for more than two decades. Metabolic responses to substitution of fishery products have been shown to impact growth performance and immune system of fish as well as their subsequent nutritional value, particularly in marine fish species, which exhibit low capacity for biosynthesis of long-chain poly-unsaturated fatty acids (LC-PUFA). The main objective of the present study was to analyse the effects of a plant-based diet on the hepatic transcriptome of European sea bass (Dicentrarchus labrax).ResultsWe report the first results obtained using a transcriptomic approach on the liver of two half-sibfamilies of the European sea bass that exhibit similar growth rates when fed a fish-based diet (FD), but significantly different growth rates when fed an all-plant diet (VD). Overall gene expression was analysed using oligo DNA microarrays (GPL9663). Statistical analysis identified 582 unique annotated genes differentially expressed between groups of fish fed the two diets, 199 genes regulated by genetic factors, and 72 genes that exhibited diet-family interactions. The expression of several genes involved in the LC-PUFA and cholesterol biosynthetic pathways was found to be up-regulated in fish fed VD, suggesting a stimulation of the lipogenic pathways. No significant diet-family interaction for the regulation of LC-PUFA biosynthesis pathways could be detected by microarray analysis. This result was in agreement with LC-PUFA profiles, which were found to be similar in the flesh of the two half-sibfamilies. In addition, the combination of our transcriptomic data with an analysis of plasmatic immune parameters revealed a stimulation of complement activity associated with an immunodeficiency in the fish fed VD, and different inflammatory status between the two half-sibfamilies. Biological processes related to protein catabolism, amino acid transaminations, RNA splicing and blood coagulation were also found to be regulated by diet, while the expression of genes involved in protein and ATP synthesis differed between the half-sibfamilies.ConclusionsOverall, the combined gene expression, compositional and biochemical studies demonstrated a large panel of metabolic and physiological effects induced by total substitution of both FM and FO in the diets of European sea bass and revealed physiological characteristics associated with the two half-sibfamilies.