Identification of a major locus determining a pigmentation defect in cultivated gilthead seabream (Sparus aurata).

The gilthead seabream (Sparus aurata) is an important cultivated species in the Mediterranean area. A major problem for the gilthead seabream aquaculture sector derives from the high frequency of phenotypic abnormalities, including discolorations. In this study, we applied a whole-genome resequencing approach to identify a genomic region affecting a pigmentation defect that occurred in a cultivated S. aurata population. Two equimolar DNA pools were constructed using DNA extracted from 30 normally coloured and 21 non-pigmented fish collected among the offspring of the same broodstock nucleus. Whole-genome resequencing reads from the two DNA pools were aligned to the S. aurata draft genome and variant calling was performed. A whole-genome heterozygosity scan from single pool sequencing data highlighted a peak of reduced heterozygosity of approximately 5 Mbp on chromosome 6 in the non-pigmented pool that was not present in the normally coloured pool. The comparison of the non-pigmented with the normally coloured fish using a whole-genome FST analysis detected three main regions within the coordinates previously detected with the heterozygosity analysis. The results support the presence of a major locus affecting this discoloration defect in this fish population. The results of this study have practical applications, including the possibility of eliminating this defect from the breeding stock, with direct economic advantages derived from the reduction of discarded fry. Other studies are needed to identify the candidate gene and the causative mutation, which could add information to understand the complex biology of fish pigmentation.