Effects of Dietary Antioxidants on Oxidative Status and Disease Resistance in the Pacific Whiteleg Shrimp Litopenaeus vannamei

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Petty, Aaron Christopher
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Three studies were performed to assess whether dietary antioxidants ethoxyquin or astaxanthin improved oxidative status, disease resistance and/or growth in juvenile Pacific whiteleg shrimp, Litopenaeus vannamei. The potential detrimental effects of including oxidized oils in shrimp diets were examined using the same metrics of growth, oxidative status and immune defense. For each diet study testing the ethoxyquin blend (Diet Study I, II), shrimp were fed one of four diet regimens for 4 weeks (Diet Study I) or 6 weeks (Diet Study II). Two of the diets contained oxidized menhaden oil (peroxide value 200 meq/kg) to assess the impact of oxidized oil in shrimp rations. In the third study, shrimp were fed diets with or without the carotenoid astaxanthin for 8 weeks. Both astaxanthin diets incorporated oxidized menhaden oil, and lacked supplemental vitamin E. In all three studies animal weights and resistance to challenge with the bacterium Vibrio campbellii were measured periodically over the course of the study. At the conclusion of each study, oxidative damage and stress was measured in the hepatopancreas of each diet group using assays for lipid peroxidation (LPx) and glutathione (GSH). When included in the diet of juvenile L. vannamei neither the ethoxyquin blend nor astaxanthin had a significant impact on growth, resistance to bacterial disease, levels of oxidative damage or oxidative stress. However, levels of LPx, measured as thiobarbituric acid reactive substances (TBARS) were significantly higher in shrimp fed diets containing highly oxidized menhaden oil without vitamin E than in animals fed fresh oil diets. A temporal decline in immunocompetence was also observed across Diet Studies I and II, suggesting that the bacterial challenge assay has sufficient power to reveal changes in immunocompetence, and that an unknown stressor is to blame for the observed decline. Although the present study did not reveal any significant changes in regard to antioxidant supplementation, disease remains a problem in shrimp aquaculture, and dietary supplementation with antioxidants should theoretically be a promising disease prevention option for increasing resistance of shrimps to pathogens.
Whiteleg shrimp -- Immunology; Whiteleg shrimp -- Nutrition; Shrimps -- Diseases