Detection of QTL influencing cortisol levels in rainbow trout (Oncorhynchus mykiss)

Abstract

Genetic variation in sensitivity to stress is a major determinant of production and welfare of aquaculture species. We investigated the genetics of the stress response using rainbow trout (Oncorhynchus mykiss) clonal lines with differing levels of domestication. First, we compared levels of cortisol among three clonal lines: two derived from highly domesticated populations (Arlee and OSU) and one from a population recently taken into captivity (Swanson). The Arlee clonal line showed significantly reduced cortisol levels in response to a netting stressor relative to the OSU and Swanson clonal lines. Next, we used interval mapping and composite interval mapping to scan the genome for quantitative trait loci (QTL) influencing post-stress cortisol levels in doubled haploid offspring of an OSU × Arlee hybrid and compared these to QTL for body mass. Two significant QTL with opposing additive effects on cortisol levels were detected, explaining 43% of the phenotypic variation. Two QTL were also detected for juvenile body mass, one of which overlapped with a QTL for cortisol levels on linkage group OA-XXVII, indicating a possible genetic link between these traits. However, the additive effects of these overlapping QTL suggest a positive relationship between cortisol levels and growth rate rather than the expected negative relationship. Our findings suggest complex genetic control of stress physiology and its relationship with growth rate.