Journal of Fish Biology (2009) 75, 1895–1905 doi:10.1111/j.1095-8649.2009.02433.x, available online at www.interscience.wiley.com Preliminary examination of oxidative stress in juvenile spring Chinook salmon Oncorhynchus tshawytscha of wild origin sampled from transport barges T. L. Welker*† and J. L. Congleton‡ *Aquatic Animal Health Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Auburn, AL 36832-0952, U.S.A. and ‡Idaho Cooperative Fish and Wildlife Research Unit, United States Geological Survey, College of Natural Resources, University of Idaho, Moscow, ID 83844-1141, U.S.A. (Received 12 August 2008, Accepted 7 August 2009) Migrating juvenile wild Chinook salmon Oncorhynchus tshawytscha, collected and loaded onto transport barges at Lower Granite Dam on the Snake River, were sampled from barges at John Day Dam, 348 km downstream, at 5 day intervals beginning in late April and ending in late May. An increase in lipid peroxidation and decrease in vitamin E in liver were observed from early to late in the barge transportation season. These changes seemed unrelated to changes in plasma cortisol or corresponding glucose levels, which declined from early to late in the season, or the concentration of n-3 highly unsaturated fatty acid (HUFA) concentrations in tissue but may be related to water temperature, which increased during the transport season, or other changes associated with the parr–smolt transformation. Journal compilation © 2009 The Fisheries Society of the British Isles No claim to original US government works Key words: cortisol; dam passage; HUFA; lipid peroxidation; vitamin E. Construction of hydroelectric dams on the Snake and Columbia Rivers and their trib- utaries has greatly altered the riverine ecosystem (National Research Council, 1996) and produced conditions deemed unfavourable for emigrating juvenile salmonids (e.g. increased travel time, elevated water temperature, exposure to predators, pas- sage through hydroelectric turbines and gas supersaturation). To reduce exposure to unfavourable conditions in the Snake–Columbia River hydrosystem, juvenile salmonids are collected at Lower Granite, Little Goose and Lower Monumental Dams on the Snake River and McNary Dam on the Columbia River, loaded onto trucks or barges, and transported and released at a site that is 235 km upstream of the mouth of the Columbia River (Ward et al ., 1997). Although transportation reduces exposure to the hydrosystem, it may adversely affect emigrants by poten- tially increasing horizontal transmission of pathogens (Maule et al ., 1988) or by elevating stress levels (Maule et al ., 1988; Schreck et al ., 1989; Congleton et al ., 2000). In addition, migrating smolts are undergoing physiological changes as a result †Author to whom correspondence should be addressed. Tel.: +1 334 887 3741; fax: +1 334 887 2983; email: thomas.welker@ars.usda.gov 1895 Journal compilation © 2009 The Fisheries Society of the British Isles No claim to original US government works