Cortisol Response to a Crowding Stress: Heritability and Association with Disease Resistance to Yersinia ruckeri in Rainbow Trout

Abstract

The U.S. Department of Agriculture's National Center for Cool and Cold Water Aquaculture is conducting a breeding program for rainbow trout Oncorhynchus mykiss to develop improved germplasm for the U.S. aquaculture industry. Current selection efforts are focused on growth and disease resistance, but stress response is also a concern. Using plasma cortisol concentrations after a 3-h crowding stress as a measure of stress responsiveness, we have previously shown family variation in cortisol responsiveness and a positive phenotypic correlation between poststressor cortisol level and growth performance within our broodstock. Selection for improved growth performance may therefore increase cortisol responsiveness to stress. In the present studies, narrow-sense heritability (h ²) for cortisol responsiveness was estimated to be moderately high by means of midparent–offspring regression and nested family design analyses (h ² ≥ 0.40 and 0.56, respectively). In addition, fish from the same families were used to determine associations between cortisol responsiveness to crowding and resistance to Yersinia ruckeri, the pathogenic agent of enteric redmouth disease, in an immersion challenge. Phenotypic and breeding values for cortisol responsiveness were not correlated with survivability with respect to Y. ruckeri whether or not the fish experienced repeated daily exposure to a crowding stress before the disease challenge. Furthermore, phenotypic and breeding values for poststressor plasma glucose and chloride levels and lysozyme activity did not correlate with disease survivability in stressed and unstressed fish. Finally, there was no correlation between the survival values of families when they were stressed before the disease challenge and when they were not, suggesting that there is variability among families in the effect of stress on resistance to Y. ruckeri.