The majority of the genetic studies in aquaculture breeding programs focus on commercial traits such as body weight, morphology, and resistance against diseases. However, studying stress response in European seabass may contribute to the understanding of the genetic component of stress and its future use to select broodstock whose offspring may potentially be less affected by handling. A total of 865 European seabass offspring were used to measure body weight and stress response. Moreover, a disease challenge experiment with Vibrio anguillarum was conducted in a subset (332) of the above fish to study disease resistance. Fish were genotyped with a 57k SNP array, and a Genome-Wide Association study (GWAS) was performed. Five SNPs were found to be statistically significant, three of which affect stress indicators and body weight (in a subgroup of the population), and a putative SNP affects growth performance, while no SNP associated with resistance to Vibrio was found. A moderate to high genomic heritability regarding stress indicators and body weight was estimated using the Restricted Maximum Likelihood (REML) process. Finally, the accuracy, along with the correlation between Estimated Breeding Values (EBVs) and Genomic Estimated Breeding Values (GEBVs), were calculated for all the traits.

Background/Objectives: In gilthead seabream, the transition from fish meal/oil-based diets to diets with partial plant-based replacement is gaining ground due to price fluctuations and environmental concerns. Most studies focus on the dietary effects on important commercial traits such as body weight and fat deposition, while metabolic traits and their underlying genetic and transcriptional regulation remain largely unexplored. Methods: In the present study, the response of metabolic traits (protein, cholesterol, and triglycerides levels) was measured in gilthead seabream of different genetic backgrounds at 15 (D15) and 30 days (D30) after a shift from a fish meal/oil-based diet (FM) to a plant-based (PP) diet. Results: Moderate heritability of total protein and triglyceride content of blood was estimated on D30. Significantly positive genetic correlations were observed between triglyceride D30 content and final weight and muscle fat. No significant genotype-by-diet interaction effects were detected. At the end of the production cycle, final body weight and fat were recorded, and hepatic expressions of ghri, ghrii, igf1 and ttr genes were measured in a subpopulation of 160 fish. An overall negative correlation was recorded between the hepatic expression of igf1 and final weight, whereas strong positive correlations were observed between the expression of all hepatic genes measured. In the same population, fourteen SNPs located in the 3′ UTR of ghrii and igf1 genes were genotyped and analyzed in two ways, as a sum-of-risk score and individually as predictors for body weight, muscle fat, metabolic traits and hepatic expression levels. The sum-of-risk score was significantly associated with muscle fat and ttr expression. Studying the effect of each SNP independently, two SNPs in the igf1 gene were associated with ghrii expression levels and one SNP in igf1 gene was associated with triglyceride levels at day 15 (Trigl_D15) while one SNP in ghrii was associated with ttr expression levels. Focusing on the diet, it was significantly associated with final weight, muscle fat, protein (D30) and triglycerides levels, and hepatic expression levels of ghrii.