LANKFORD, S.E.; MILLER, R.A.; ADAMS, T.E.; CECH JR., J.J.; Univ. of California, Davis; Univ. of California, Davis; Univ. of California, Davis; Univ. of California, Davis: Hormonal, Metabolic, and Performance Based Measurements of Chronic Stress in Green Sturgeon, Acipenser medirostris

To simulate chronic stress, groups of three 0+ green sturgeon were place into flow-through, indoor tanks and stressed twice daily (1000 and 1600 h) for 28 consecutive days. Fish were exposed to two of three randomized acute stressors: a 5-min chasing stressor, a 10-min water depth reduction stressor, or a 5-min confinement stressor. These stressors stimulated a graded, acute plasma cortisol response and did not result in habituation of the acute stress response, as measured in 7-day intervals. Metabolic scope for activity (MSA), critical swimming velocity (U_crit), and liver glycogen levels were measured in fish exposed to the chronic stress regime. We hypothesized that chronic stress would increase maintenance requirements resulting in 1) increased maintenance metabolic rates (MMR), 2) decreased MSA, 3) decreased U_crit, and 4) decreased liver glycogen. Oxygen consumption and U_crit were measured using a Brett-type swimming-tunnel respirometer. Exposure to the chronic stress regime resulted in a 25% reduction of MSA due to significantly increased MMR (0.273 � 0.014 vs. 0.185 � 0.015 mg O₂ hr^-1 g^-1 chronic and control fish, respectively) supporting hypotheses 1 & 2. A 50% reduction in liver glycogen levels (supporting hypothesis 4) was also measured in chronically stressed fish, however there was no difference in U_crit between treatments (rejecting hypothesis 3). We conclude that our chronic stress regime resulted in a significant maintenance cost to green sturgeon, without decreasing their swimming performance.