QTL affecting morphometric traits and stress response in the gilthead seabream (Sparus aurata)

The gilthead seabream (Sparus aurata) is an important aquaculture species that has only been subject to an incipient selective breeding programme. This study, which examined the genetic architecture of seabream morphology and stress response to confinement, takes a step toward the use of marker assisted selection in this species. Major loci affecting these traits were mapped, using data from 460 offspring derived from seven paternal and 73 maternal half-sib families were analysed. Fish were killed following a four-hour confinement experiment to induce stress, after which 15 morphometric measurements were collected and blood was sampled for DNA extraction and plasma cortisol level determination. Heritabilities for the morphometric traits were moderate to high (0.24 – 0.58), with genetic and phenotypic correlations between the traits generally very high. However, the heritability of plasma cortisol level was not significantly different from zero.
A population-specific genetic linkage map was built for 56 microsatellite markers, comprising 16 linkage groups and ten unlinked markers. Half-sib and variance components QTL analyses detected a single genome-wide significant QTL (SaimbcF7b), a single unlinked marker explaining 13-23% of the phenotypic variance in the majority of the morphometric traits. Several other putative QTL were identified for morphometric traits (on Linkage Groups 4a, 7, 9, 18, A, C, F and I), along with two other QTL (LG10 and B) that were suggestive for stress response. Fitting body weight as a covariate for the morphometric traits resulted in three genome-wide significant QTL affecting aspects of body shape independent of overall body size. For stress response we only identified suggestive evidence for QTL. These findings contribute to understanding the genetic regulation of important economic traits in seabream.