ABSTRACT
Selenium presents an interesting paradox in the field of aquatic toxicology because it is both a nutrient and a poison. As a nutrient, it is required in the diet of fish at concentrations of about 0.1 to 0.5 /x,g/g dry weight (Hodson and Hilton, 1983; Gatlin and Wilson, 1984) (In this chapter, all dietary and tissue concentrations are reported on a dry weight basis.) Selenium is necessary for proper formation and functioning of glutathione peroxidase, which is a major cellular antioxidant enzyme (Heisinger and Dawson, 1983; Bell et al., 1986). This enzyme protects cell membranes from damage or lysis due to lipid peroxidation. Without adequate selenium, normal cellular and organ metabolism break down because of peroxides produced as a by-product of digestion. Symptoms of selenium deficiency in fish include reduced growth, anemia, exudative diathesis, muscular dystrophy, and increased mortality (Poston et al., 1976; Bell and Cowey, 1985; Bell et al., 1985; Gatlin et al., 1986). Thus, the beneficial effects of proper selenium in the diet of fish are firmly established.
