Zoological Studies 45(4): 492-502 (2006)

Appropriate feed composition is important for growth, disease resistance, and immune activi-ty in aquacultured fish. A nutritionally adequate diet satisfies 3 needs: fuel (chemical energy), the organic raw materials for biosynthesis, and a sup-ply of essential nutrients. Proteins, lipids, and car-bohydrates are the critical components of the diet for supplying the carbon skeleton and energy. Fish may convert protein into an energy source if non-protein energy sources (carbohydrates and fats) are not present in sufficient quantities in the diet. Therefore, a certain amount of lipids is usual-ly included in diets as an energy source and also to increase the protein efficiency (Cho and Kaushik 1990, Williams et al. 2003). It was also reported that increasing the level of dietary lipids beyond about 9%-10 % did not improve fish growth rates, but instead reduced the fish s appetite in humpback grouper (Cromileptes altivelis) (Williams et al. 2004). High protein requirements (Chen and Tsai 1994, Shiau and Lan 1996) and low utilization of carbohydrates and lipids in groupers have been reported (Shiau and Lin 2001 2002, Lin and Shiau 2003). So it can be inferred that groupers, marine carnivores, are adapted to using protein as the preferred energ