Salmonid Fishes Differ in Their Cortisol and Glucose Responses to Handling and Transport Stress

Uniformly acclimated juvenile salmonid fishes subjected to 30-s handling or 2-h transport stressors showed differences in the magnitude of poststress plasma cortisol and glucose increases. Lake trout Salvelinus namaycush had the highest maximum plasma cortisol after handling (143 ng/mL), rainbow trout Oncorhynchus mykiss had the lowest levels (43 ng/mL), and brown trout Salmo trutta and brook trout Salvelinus fontinalis had intermediate levels (111 and 89 ng/mL, respectively). Lake trout had the highest peak posttransport plasma cortisol (124 ng/mL) compared with brook trout (69 ng/mL) and rainbow trout (57 ng/mL). Peak posthandling plasma glucose levels were highest in brown trout (257 mg/dL) followed by brook, rainbow, and lake trout (177, 153, and 150 mg/dL, respectively). Rainbow trout, however, had the highest peak plasma glucose concentration (223 mg/dL) after transport, and lake trout the lowest (143 mg/dL). Species considered as most stressed based on plasma cortisol elevations were not necessarily so as indicated by changes in glucose. Thus, the evaluation of handling or transport stress in hatchery-reared salmonid fishes cannot rely solely on a single indicator nor on direct comparison with other species.