We tested the efficacy of using electrofishing to collect juvenile fall chinook salmon Oncorhynchus tshawytschato assess their plasma cortisol concentrations. In laboratory experiments, plasma cortisol titers offish sampled immediately (<4 s) after a 1.5-s, 500-V DC electroshock were not different from controls (mean ± SE, 28.8 ± 5.2 ng/mL), but within 15 min they were significantly higher (148.2 ± 19.0 ng/mL) than controls. Plasma cortisol levels of fish released through turbines and of those released through the juvenile-bypass system at Bonneville Dam, Oregon-Washington, and collected by electrofishing did not differ from each other or from prerelease samples (about 70 ± 7 ng/mL). Our results indicate that electrofishing can be used to collect fish for stress assessment in the wild, provided fish are sacrificed immediately after capture, We are concerned, however, that the small number of fish we captured by electrofishing may not be representative of the majority of fish that pass through turbines or bypass systems. The fish used in this study were not migrating smolts and so were not typical of juvenile chinook salmon passing through hydroelectric dams on the Columbia River. Developmental as well as species- and stock-related factors should be addressed in future studies.
