Oxidative Stress in Migrating Spring Chinook Salmon Smolts of Hatchery Origin: Changes in Vitamin E and Lipid Peroxidation

Abstract

Polar lipid peroxidation (LPO), a measure of oxidative damage to membrane lipids, and concentrations of the antioxidant vitamin E were determined for kidney and liver tissues of Chinook salmon Oncorhynchus tshawytscha sampled before release from three hatcheries in the Snake River basin, Idaho, and from juvenile fish bypass systems at several dams in the Columbia– Snake River federal hydropower system. Oxidative stress, as indicated by LPO, significantly increased in migrating juveniles after they left the hatchery in each of the study years (1999 and 2000). The largest increase in liver LPO occurred between the hatcheries and Lower Granite Dam (the first dam encountered by migrating fish) with little or no additional change as the fish migrated through the hydropower system. Kidney LPO, on the other hand, continued to increase as the fish migrated to lower Columbia River dams 348–461 km downstream. Levels of vitamin E were inversely correlated with LPO. Postrelease decreases in vitamin E were significant for kidney tissue in 1999 and for liver tissue in 2000. Liver and kidney LPO indices were higher and vitamin E concentrations were lower in 1999 than in 2000, possibly because river flows, spill levels at the dams, and dissolved gas levels in the river were higher in 1999. Liver vitamin E was significantly lower in fish exposed to juvenile fish bypass systems at two or more dams (including the dam where they were sampled) than in fish bypassed only at the sampling location; however, greater exposure to bypasses did not increase liver or kidney LPO indices. Increased polar LPO could have adverse effects on a range of physiological processes in migrating smolts. The significance of oxidative stress in migrating smolts will, however, remain uncertain until research is done to relate oxidative stress indices to biological function and fitness.