ASSOCIATIONS BETWEEN PLASMA GROWTH HORMONE, INSULIN-LIKE GROWTH FACTOR-1 AND CORTISOL, WITH STRESS RESPONSIVENESS AND GROWTH PERFORMANCE IN A SELECTIVE BREEDING PROGRAM FOR RAINBOW TROUT (ONCORHYCHUS MYKISS)

Authors: Lankford, Scott; Weber, Gregory - Greg

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2005
Publication Date: 3/21/2006
Citation: Lankford, S.E., Weber, G.M. 2006. Associations between plasma growth hormone, insulin-like growth factor-1 and cortisol, with stress responsiveness and growth performance in a selective breeding program for rainbow trout (oncorhychus mykiss). North American Journal of Aquaculture 68, 151-159.

Interpretive Summary: The National Center for Cool and Cold Water Aquaculture is conducting a selective breeding program to improve germplasm for the United States rainbow trout aquaculture industries. Two lines are being selected for improved performance including growth. In a previous study we found families of the first line that grew faster also had increased concentrations of the hormone, cortisol, following a crowding stress. This increase in blood levels of cortisol following a stress event suggests the fish are more stress responsive. Stress is a concern because stress has been shown to have negative impacts on many traits important to the aquaculture of rainbow trout including growth rate, feed efficiency, disease resistance, and reproductive performance, all of which are performance traits under consideration for improvement in our broodstock. At this point, it is still not known whether higher blood levels of cortisol following a stress is good or bad. The present study was conducted to begin to determine why some families grow faster than others and why there is a connection between growth and stress responsiveness. First, we found that the faster growing fish of a second line also had high blood levels of the stress hormone cortisol following a stress. As part of our efforts to determine why there is this connection between growth and stress responsiveness, we measured blood levels of two hormones that regulate growth in the animals, growth hormone and insulin-like growth factor-I. We did not find any connection between blood levels of these hormones and stress responsiveness. We did find that growth hormone is reduced and insulin-like growth factor-I was increased in the blood of the faster growing animals suggesting the difference in growth rate is associated with differences in the system of hormones that regulate growth. Therefore, we may be able to use differences in these hormone levels to help us decide which fish to select for breeding faster growing fish.

Technical Abstract: The National Center for Cool and Cold Water Aquaculture is conducting a selective breeding program to improve germplasm for the United States rainbow trout aquaculture industries. Two lines are being selected for improved growth. In a previous study we found a positive correlation between stress responsiveness, as indicated by plasma cortisol concentrations following a 3-hour confinement stressor, and growth performance, as indicated by body weight at selection (approximately 300 days post-hatching [dph]), for the families of the first line. This association is confirmed for the second line in the present study. 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 variation in growth performance and the basis of the association between stress responsiveness and growth performance among our germplasm. The hormone levels were compared against two measures of growth, body weight and thermal growth coefficient (TGC). Resting plasma IGF-I and GH levels were not associated with stress responsiveness, thereby providing no link between stress responsiveness and growth performance. Nevertheless, resting plasma GH and cortisol were negatively correlated, and IGF-I positively correlated with TGC, whereas only GH was correlated with body weight at 297 dph. In addition, TGC was better at predicting growth performance at 459 dph, than was body weight at 297 dph. Our findings suggest the genetic variation in growth performance among our broodstock families can be explained by alterations in the growth regulatory axis.