Stress Indices in Migrating Juvenile Chinook Salmon and Steelhead of Wild and Hatchery Origin before and after Barge Transportation

Abstract
Migrating wild (W) and hatchery-reared (H) chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss juveniles were sampled after loading into fish-transport barges at Lower Granite Dam on the Snake River, Washington, and after barge transportation downstream to Bonneville Dam on the Columbia River. Stress indices (increased plasma cortisol and glucose concentrations and decreased plasma chloride concentrations) were higher (P < 0.001) for chinook salmon sampled during midseason (early to mid-May), when fish loading densities in barges were at seasonal maximums, than were stress indices for those sampled earlier or later. Cortisol concentrations in chinook salmon were correlated with steelhead densities after loading of barges (P < 0.0001, R 2 = 0.41) and after arrival of barges at Bonneville Dam (P < 0.0001, R 2 = 0.65). Cortisol concentrations were not correlated with gill Na+, K+–adenosine triphosphatase activities, which were higher in W than in H fish of both species. Cortiso...

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