Evaluation of a Stress Response for Use in a Selective Breeding Program for Improved Growth and Disease Resistance in Rainbow Trout

Abstract

A breeding program to develop improved germplasm for the U.S. rainbow trout Oncorhynchus mykiss aquaculture industry is being conducted at the U.S. Department of Agriculture's National Center for Cool and Cold Water Aquaculture. Although current selection efforts are based on growth and disease resistance, stress responsiveness is also a concern. Previous work has shown that heritable differences in stress response can be identified by measuring blood levels of cortisol after exposure to a 3-h crowding stress. We characterized this stress response and measured plasma glucose concentrations in 64 of our broodstock families. We found the method reliable for identifying differences in this stress response. Values for both cortisol and glucose response were similar for replicates of families. The size of the fish within the range examined and the sex of the animals, which were reproductively immature, did not appear to affect response. Variation in poststressor plasma cortisol and glucose was observed among families (11.6–93.9 ng cortisol/mL and 5.2–10.9 mM glucose) and individuals. The cortisol and glucose responses to the stressor were not correlated. Resting and poststressor plasma cortisol concentrations were significantly correlated among families, but glucose concentrations were not. Survival rate was 70% and there was no association between survival and poststressor cortisol or glucose concentration. There was a significant positive association between cortisol response and growth performance, and mean plasma cortisol concentrations in response to the stress challenge were significantly greater for families selected for faster growth rate than for those not selected.