Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2001
Publication Date: 1/1/2001
Citation: DAVIS JR, K.B., SIMCO, B.A., LI, M., ROBINSON, E. EFFECT OF CONSTANT AND FLUCTUATING TEMPERATURE ON THE CORTISOL STRESS RESPONSE. JOURNAL OF THE WORLD AQUACULTURE SOCIETY. 2001. v. 32. p. 422-425. Interpretive Summary: Many aquaculture practices induce a stress response in fish, which is characterized by the secretion of cortisol, a gluconeogenic steroid hormone. Most experiments on the cortisol response to stress have been done under constant water temperatures. Shallow ponds used in aquaculture of channel catfish can change temperature dramatically during the day. The experiments presented here report the plasma cortisol response to a confinement stressor in channel catfish held at constant temperatures and under daily temperature cycles typical of spring/fall 59-79 F and summer 76 #95 F temperatures. Fish held at a constant 95 F had higher cortisol concentrations before confinement than the other groups and cortisol did not increase due to confinement as it did in all other groups. The data suggest that constant exposure to 95 F induced a maximum cortisol synthesis and secretion and the fish were unable to respond to an additional stressful conditions. This condition is known as inadequate adrenal reserve to indicate the inability of cortisol levels to increase due to additional stress. This suggests that cultured fish derive benefit from decreased nocturnal temperatues during the summer which restores the normal stress response capability.
Technical Abstract: Initial and confinement induced changes of plasma cortisol were measured in channel catfish Ictalurus punctatus acclimated to constant temperatures, a spring/fall diurnal pattern between 15 and 26 C, and a summer diurnal pattern between 24 and 35 C. Temperature changes were achieved in 10 hours and held constant for two hours before reversing the temperature. Fish held in the spring/fall pattern or at a constant temperature revealed no difference, due to acclimation temperature in the initial cortisol concentrations, but hormone concentrations in all groups increased by about 4.5 fold following a two hour confinement. Fish held on a summer diurnal pattern had differences in both the initial cortisol samples and those after confinement. Acclimation to a constant 35 C resulted in significantly higher initial cortisol concentrations but these levels did not increase due to confinement. The inability of the fish held at 35 C to respond to the confinement was thought to be due to the constant thermal stress, resulting in an inadequate adrenal reserve.