Protein requirements of young grey mullet, Mugil capito

Abstract

The protein requirements of young grey mullet, Mugil capito, were studied by using five semi-purified diets with a casein, defatted fish meal and corn starch base, containing 12 to 60% protein, in increments of 12%, and fed for 97 days to young Mugil capito of average initial weight 2.5 g. The food conversion factor decreased with increasing dietary protein level, although not significantly above the level of 24%. Specific growth rates were proportional to the protein content of the diet up to an incorporation rate of about 24%; beyond this level specific growth rates decreased. Protein efficiency ratio and protein retention (%) decreased with increasing dietary protein level, while carcass composition was little affected. High levels of carbohydrate in the diet caused a high glycogen content in the liver, resulting in its enlargement. Mugil capito seems to require about 24% of protein for maximum growth at 23°C. These results are discussed in relation to those reported for other species of fish.