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Title: Effect of dietary alpha-tocopherol, ascorbic acid, selenium, and iron on oxidative stress in sub-yearling Chinook salmon (Oncorhynchus tshawytscha)

Author
item Welker, Thomas
item CONGLETON, JAMES - IDAHO COOP FISH & WILDLIF

Submitted to: Journal of Animal Physiology and Animal Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2007
Publication Date: 7/1/2008
Citation: Welker, T.L., Congleton, J.L. 2009. Effect of dietary alpha-tocopherol,acorbic acid, selenium, and iron on oxidative stress in sub-yearling Chinook Salmon (Oncorhynchus tshawytscha). Journal of Animal Physiology and Animal Nutrition. 93: 15-25.

Interpretive Summary: Oxidative stress has been identified as a causative agent in a number of pathologies and diseases in fish. Organisms possess enzyme systems and small-molecular-weight molecules with antioxidant capabilities that are capable of neutralizing ROS and protect against the adverse effects of oxidative stress. However, nutrition plays an important role in countering oxidative stress with several vitamins and minerals important in the antioxidant defenses of aquatic organisms. The optimum dietary levels of most antioxidant vitamins and minerals are unknown for most fish species in relation to oxidative stress. The antioxidants alpha-tocopherol + ascorbic acid (TOCAA) and selenium (Se) and pro-oxidant iron (Fe) were supplemented in the diets of juvenile spring Chinook salmon on to determine the effect on indices of oxidative stress. Oxidative damage in liver and kidney and red blood cells (RBC) was determined after feeding experimental diets for 16 (early December) and 28 (early March) weeks. Only TOCAA influenced oxidative stress in this study, with most measures of oxidative damage decreasing with increasing levels of TOCAA. We also observed a TOCAA-stimulated increase in susceptibility of RBCs to oxidative damage in March at the highest levels of TOCAA. The data suggest that under most circumstances a progressive decrease in oxidative stress occurs as dietary TOCAA increases, but higher TOCAA concentrations can stimulate tissue damage in some situations. Higher levels of TOCAA in the diet were required in March than in December to achieve comparable levels of protection against oxidative damage, which may have been due to physiological changes associated with the parr-smolt transformation. Red blood cells appeared to be more sensitive to variation in dietary levels of TOCAA than liver and kidney tissues. We propose that a TOCAA level of approximately 350-600 mg kg-1 diet would provide adequate protection against oxidative stress under most circumstances in juvenile Chinook salmon.

Technical Abstract: A three-variable central composite design coupled with surface-response analysis was used to examine the effects of dietary alpha-tocopherol + ascorbic acid (TOCAA), selenium (Se), and iron (Fe) on indices of oxidative stress in juvenile spring Chinook salmon. Each dietary factor was tested at five levels for a total of fifteen dietary combinations (diets). Oxidative damage in liver and kidney (lipid peroxidation, protein carbonyls) and erythrocytes (erythrocyte resistance to peroxidative lysis, ERPL) was determined after feeding experimental diets for 16 (early December) and 28 (early March) weeks. Only TOCAA influenced oxidative stress in this study, with most measures of oxidative damage decreasing (liver lipid peroxidation in December and March; ERPL in December; liver protein carbonyl in March) with increasing levels of TOCAA. We also observed a TOCAA-stimulated increase in susceptibility of erythrocytes to peroxidative lysis in March at the highest levels of TOCAA. The data suggest that under most circumstances a progressive decrease in oxidative stress occurs as dietary TOCAA increases, but higher TOCAA concentrations can stimulate oxidative damage in some situations. Higher levels of TOCAA in the diet were required in March than in December to achieve comparable levels of protection against oxidative damage, which may have been due to physiological changes associated with the parr-smolt transformation. Erythrocytes appeared to be more sensitive to variation in dietary levels of TOCAA than liver and kidney tissues. Using the March ERPL assay results as a baseline, a TOCAA level of approximately 350-600 mg/kg diet would provide adequate protection against lipid peroxidation under most circumstances in juvenile Chinook salmon.