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Abstract In order to investigate optimum dietary protein requirement, juvenile mangrove red snapper Lutjanus argentimaculatus (body weight 8.0±0.3 g) were reared in seawater tanks (125 liters each) and fed one of the experimental diets at a daily ration of 2% body weight for 90 days. Six isoenergetic (22.4 kJg-1) diets were formulated to contain protein levels of 20%, 25%, 30%, 35%, 40% and 45%. Fish fed diets of 40% and 45% protein produced higher weight gain and growth rate than those of the other diets. Broken line regression analysis yielded an optimal protein level of 42.8%. Fish whole body, muscle, liver and visceral composition showed that moisture content of fish fed diets of 40% and 45% protein was significantly higher than that of fish fed diets containing protein levels of 20% to 35% in 5% increments, although the lipid contents were lower. No significant difference was observed in protein and ash contents of whole fish or body organs for the diets of 20% to 45% protein.
Fish fed 40% and 45% protein diets showed higher nitrogen gain and nitrogen retention efficiency than those fed on other diets. The mesenteric fat, hepato- and viscerosomatic indices of fish fed diets of 40% and 45% protein were significantly higher than those of fish fed diets of 20%, 25%, 30% and 35% protein. Based on the biological data, it was estimated that the optimal level of protein for L. argentimaculatus weighing between 8.0 g and 110 g was 40% to 42.8%.
Key words: Mangrove red snapper, growth, protein requirements, nutrient retention, body composition.
INTRODUCTION The mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775) is a marine carnivorous fish that has been identified as a potential candidate for aquaculture in South-east Asia, Southern China and the Middle East (Emata et al., 1994; Leung et al., 1999; Estudillo et al., 2000; Catacutan et al., 2001; Emata, 2003; Catacutan and Pagador, 2004). In Pakistan, it is known for its good quality meat. Owing to its rapid growth and high commercial value (Anonymous, 2002), there is an interest in its culture (Abbas, 2002; Abbas and Siddiqui, 2009). The sustainable aquaculture of this fish depends on nutritionally balanced fish feed. Since protein is the most expensive component in fish feed, optimizing dietary concentration is essential...