Investigating the Impact of six6 Genetic Variation on Morphological Traits in Larvae and Juveniles of European Seabass (Dicentrarchus labrax Linnaeus)

The European seabass is a key Mediterranean aquaculture species, vital for sustainably meeting rising global protein demands amid declining wild fish stocks. Genetic analyses have identified the six6 gene as a candidate target of domestication and selective breeding, with two SNPs showing significant genotypic differences between wild and farmed European seabass populations. Further analyses revealed differential six6 expression between larval and juvenile stages, suggesting a potential developmental role. This study explores associations between these SNPs and important aquaculture traits across early developmental stages. Seabass samples were examined at 34 days post-hatching (dph, larval stage) and 71 dph (juvenile stage). We examined associations between specific six6 SNPs and morphological traits using traditional morphometrics, analyzing 20 and 26 characteristics in the larval and juvenile stages, respectively. Shape and size differences were examined with allometric correction. The six6 gene was primarily associated with body length, height, and caudal fin morphology. Notably, homozygous six6 genotype combinations at the studied SNPs were associated with increased body length in a developmental stage-specific manner. Variation in this gene also appeared to influence eye development in juveniles. These findings offer phenotypic evidence supporting previous genetic and expression studies in European seabass, highlighting their potential applications in fisheries and aquaculture.