Zinc is an essential element many functions are recognized such as it is an essential part or a cofactor for a number of enzymes including carbonic anhydrase, carboxypeptidase, superoxide dismutase, lactate dehydrogenase, phosphatase and glutamate dehydrogenase (Prosser and Brown, 1966, Williams, 1969 and NRC, 1993). As a component of carbonic anhydrase, zinc playes a role in binding carbon dioxide in teleost cells, combining it with water to form carbonic acid and releasing carbon dioxide from capillaries at secondary lamellae of gills. Also, carbonic anhydrase is important in maintaining acid-base balance in renal tubule cells. As a cofactor of the protein-splitting enzyme carboxypeptidase, zinc has a key role in protein digestion (Sorensen, 1991). Fish accumulate zinc from both water and dietary sources; however, dietary zinc is more efficiently absorbed (Hardy et al., 1987). The zinc requirement of young rainbow trout and carp is 15 to 30 mg/kg of diet (Ogino and Yang, 1978 and 1979), wherease blue tilapia require 20 mg/kg of diet (McClain and Gatlin, 1988). Dietary protein source, phytic acid and form od zinc and calcium affect zinc absorption and use in fish (Hardy and Shearer, 1985, Wekell et al., 1986, Satoh et al., 1987 and 1989 and McClain and Gatlin, 1988). The bioavailability of zinc in fishmeal is inversely related to the tricalcium phosphate content. This is presumably caused by absorption of zinc into insoluble calcium phosphate complexes in the intestine that are passed through the gut unabsorbed and excreted (Satoh et al., 1987).