Associations between plasma growth hormone, insulin-like growth factor-I, and cortisol with stress responsiveness and growth performance in a selective breeding program for rainbow trout

The National Center for Cool and Cold Water Aquaculture is conducting a selective breeding program to improve the germplasm of rainbow trout Oncorhynchus mykiss for aquaculture. Two lines are being selected for improved growth. We previously found a positive correlation between stress responsiveness, indicated by plasma cortisol concentration after a 3-h confinement stressor, and growth performance, indicated by body weight at selection (approximately 300 d posthatching [dph]). in families from the first line. This correlation is confirmed for the second line in the present study. In addition to stressor-induced cortisol levels, resting plasma growth hormone (GH), insulin-like growth factor-I (IGF-I). and cortisol concentrations were measured in the second line as a first step in determining the physiological and genetic bases for growth performance variation and the association between stress responsiveness and growth performance in our germiplasm. Hormone levels were compared against two measures of growth: body weight and thermal growth coefficient (TGC). Plasma concentrations of IGF-I and GH in resting fish were not correlated with stress responsiveness and thus provided no link between stress responsiveness and the growth regulatory axis. The TGC was negatively correlated with resting plasma GH and cortisol and positively correlated with IGF-I, whereas only GH was correlated with body weight at 297 dph. Our results suggest that the variation in growth performance among our broodstock families is explained, in part. by variations in resting levels of the growth regulatory and stress axes. In addition, TGC more accurately predicted future growth-body weight at 459 dph-than did body weight at 297 dph.