PROTEIN-SPARING EFFECT BY CARBOHYDRATES IN DIETS FOR TILAPIA, OREOCHROMIS-NILOTICUSXO AUREUS

To investigate the utilization of different carbohydrate sources and t he possible substitution of carbohydrate for dietary protein for tilap ia, Oreochromis niloticus x O. aureus, nine approximately isoenergetic purified diets were prepared. Three dietary protein levels (32, 28, 2 4%) were achieved by substitution with three levels (33, 37, 41%) and three sources (glucose, dextrin, starch) of dietary carbohydrate. Resu lts indicated that fish fed starch or dextrin had significantly (P < 0 .05) higher weight gain and feed efficiency ratio (FER) than those fed glucose for all the protein levels with the exception of weight gain for the 24% protein level in which the difference was not significant. Fish fed starch and dextrin had similar weight pin in the 28% and 24% protein levels but were significantly (P < 0.05) lower than those in the 32% protein level. Fish fed the glucose diets with the three prote in levels had similar weight gain. Protein deposition was lower in fis h fed the glucose diets with 32% protein than with 28% or 24% protein. These data suggest that starch and dextrin are better utilized by til apia than glucose. Decreasing the dietary protein level from 28% to 24 % by increasing the starch or dextrin content in the diet from 37% to 41% did not reduce (P > 0.05) weight gain and FER, suggesting that sta rch or dextrin could spare some protein when the dietary protein level is low.