Validation of growth-related quantitative trait loci markers in turbot (Scophthalmus maximus) families as a step toward marker assisted selection

Turbot (Scophthalmus maximus) is a valuable flatfish with current selection programs to increase growth rate in the fifth generation. Disentangling the genetic architecture of growth traits has biological and productive relevance. Growth-related quantitative trait loci (QTL) and associated markers have been previously reported in turbot. Here, we tested the performance of 39 markers associated with three growth-related traits (body weight (BW), body length (BL) and condition factor (FK)) in 18 families for their potential application in marker assisted selection (MAS) in this species. A cost-effective selective genotyping approach was developed by checking the statistical power of small samples at the extreme of the phenotypic distributions. Associations between growth traits and markers were performed using two statistical approaches (contingency chi-square tests and stepwise regression analysis) to identify the most robust set of markers. Twenty markers were detected by both methods, mostly linked to previously reported growth-related QTL and encompassing 11 linkage groups (LGs). The stepwise regression analysis revealed that a subset of seven markers explained nearly 40% and 60% of the phenotypic variation at genotypic and allelic level, respectively, for BW and BL. Seven markers for BW and BL and other two for FK showed association at population level, when all family data were pooled. Validated markers might be useful to go a step forward to improve growth performance through more refined MAS, and as physical anchors for identifying causal genes underpinning growth traits in turbot.