Effects of dietary protein on growth and body composition of Nile tilapia,Oreochromis niloticus L.

The effects of dietary protein (25%, 30%, 35%, 40% and 45%) on growth, surv ival, feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were investigated for four sizes (0.51, 45, 96 and 264 g) of Ni le tilapia, Oreochromis niloticus L. In all four experiments, there was a p rogressive increase in growth with increasing dietary protein. In fry (0.51 g), significantly higher growth, survival and feed conversion were recorde d for fish fed 40-45% rather than 25-35% protein diets. Similar trends for growth and FCR were also noted in 45 g fish. For larger (96 and 264 g) tila pia, significant differences in growth and FCR were found only between fish fed 25% and 30-45% protein diets. FCR and PER decreased with increasing we ight of fish, and both were found to be negatively correlated with dietary protein level. Whole-body composition of the smallest fish was significantl y influenced by dietary protein content. Percentage body protein of the fis h fed 40-45% protein was higher than that of fish fed 25-35% protein diets, whereas lipid content decreased with increasing dietary protein level. In 45 g fish, both protein and lipid contents were higher in fish fed 25% and 30% protein diets than in those fed 35-45% protein diets. In larger tilapia , no significant influence of dietary protein level on body protein content was found. Percentage lipid decreased with increasing dietary protein leve l, and no definite trends in ash content were found. The results of these s tudies indicate that O. niloticus fry (0.51 g) should be reared on a practi cal diet containing 40% protein, and larger tilapia (96-264 g) on a diet co ntaining 30% protein.