Submitted to: North American Journal of Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2007
Publication Date: 10/30/2008
Citation: Weber, G.M., Vallejo, R.L., Lankford, S.E., Silverstein, J., Welch, T.J. 2008. Cortisol Response to a Crowding Stress: Heritability and Association with Disease Resistance to Yersinia ruckeri in Rainbow Trout. North American Journal of Aquaculture. Interpretive Summary: A breeding program to develop improved germplasm for the US rainbow trout aquaculture industry is being conducted at the USDA-ARS National Center for Cool and Cold Water Aquaculture. Current selection efforts are based on growth and disease resistance, but stress response is also a concern. Cortisol is the main stress hormone in fish. We have previously shown variation in blood levels of cortisol following a crowding stress, among our broodstock families. We have also shown a positive correlation between this measure of cortisol responsiveness and growth performance. In the present studies we estimated the heritability of the cortisol response and found it to be moderate to high (h2 > 0.40), so we are likely increasing cortisol responsiveness as we select for improved growth. Stress is associated with disease susceptibility, so we assessed if cortisol responsiveness was associated with resistance to enteric redmouth disease. We found no association whether the fish were not stressed before being exposed to the disease or first experienced repeated daily exposure to a crowding stress. Furthermore, resistance to enteric redmouth disease was not correlated with other measures of stress including post-stressor blood levels of glucose, chloride and lysozyme activity. Our findings suggest that selecting for improved growth will not necessarily affect disease resistance. We did find that the families that were the most resistant to enteric redmouth disease when challenged with the disease without being stressed were not necessarily the most resistant if the fish were stressed before being exposed to the disease. Incorporation of a stress component to the disease challenge might therefore be considered if stress is commonly associated with outbreaks of a disease for which resistance is being selected.
Technical Abstract: A breeding program to develop improved germplasm for the US rainbow trout aquaculture industry is being conducted at the USDA-ARS National Center for Cool and Cold Water Aquaculture. Current selection efforts are focused on growth and disease resistance, but stress response is also a concern. Using plasma cortisol concentrations following a 3-h crowding stress as a measure for stress responsiveness, we have previously shown family variation in cortisol responsiveness among our broodstock, and a positive phenotypic correlation with growth performance. Selection for improved growth performance may therefore increase cortisol responsiveness to stress. In the present studies, narrow-sense heritability for cortisol responsiveness was estimated to be moderately high, h2 > 0.40, using offspring-midparent regression and nested family design analyses. 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 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 post-stressor plasma glucose and chloride levels, and lysozyme activity, did not correlate with disease survivability in stressed and unstressed fish. Finally, there was no correlation for either survival days or survival breeding values when comparing families stressed versus unstressed before the disease challenge, suggesting a family by stress interaction for survivability to Y. ruckeri.