Optimum contribution of dietary protein: energy ratio in the grey mullet (Mugil cephalus, linnaeus, 1758) diets
Egyptian Journal of Aquatic Biology and Fisheries
Protein Energy Lipid Carbohydrate growth performance feed efficiency The effect of varying dietary protein and energy levels on the growth performance, feed efficiency and tissue chemical composition by increasing dietary energy sources (lipids and carbohydrates) for flathead grey mullet, Mugil cephalus fingerlings were evaluated. Twelve experimental diets were formulated by four different dietary protein levels (25, 30, 35 and 40) combined with three different gross energy levels (16, 17 and
... evels (16, 17 and 18MJ/kg diet) to provide 12 different dietary protein: energy ratios (15.43, 14.40, 13.64, 18.60, 17.46, 16.42, 21.63, 20.73,19.20, 24.26, 23.02 and 21.79 MJ/kg diet). The present results showed that, the highest final body weight, weight gain, specific growth rate, feed efficiency and protein efficiency ratio values were recorded with increasing of dietary protein levels from 25 up to 35%, irrespective of dietary energy levels. However, irrespective of dietary protein levels, the increasing dietary energy levels (from 16 to18 MJ/Kg diet) obtained slightly final body weight, weight gain, specific growth rate, feed efficiency and protein efficiency ratios. Feed conversation ratio values decreased (P≥0.05) either with increasing dietary crude protein or dietary energy levels. The best FCR value was recorded with dietary energy 18 MJ/kg and 35% protein. No statistical differences (P>0.05) were observed for the effect of dietary protein energy ratios on whole body proximate analysis except for body ether extract contents. The body lipid deposition may indicate that, when dietary lipid was supplied in excess, a proportion of this lipid was deposit as fats. Concomitant increase (P<0.05) of body lipid and protein retained were observed with increase dietary lipid levels, while negative effect on energy retained was recorded with increase energy levels. These results suggested that the diet contains 30% crude protein with 18MJ/kg -1 gross energy enhanced the growth performance and feed efficiency of Mugile cephalus, had protein-sparing effect and increased the utilization of each dietary protein and energy sources.