EFFECT OF SOURCES AND LEVELS OF PROTEIN IN DIETS OF TILAPIA (SAROTHERODON GALILAEUS ) FINGERLINGS ON THE DIGESTIBILITY OF NUTRIENTS

This study was planned to investigate the effect of three sources and levels of protein In fish diets on the digestibility coefficients on Tilapia galilae ( average body weight 4.7g ) reared in aquarium under laboratory condition. Nine diets representing three protein sources, animal, plant and mixture of animal and plant protein sources at three protein levels 22, 27 and 32% within each source were tested. The obtained results revealed that:, 1-Fish fed on plant protein source as a sole source resulted in the significant (P<0.05) higher value of digestion coefficient of dry matter ( 91.93% ) , nitrogen free extract ( 75.12% ) and energy (75.88%), while, fish fed on animal plus plant protein source showed the best significant (p < 0.05) values of digestibility of crude protein ( 87.18%) and ether extract 90.55% ). 2-Level of 22% crude protein resulted in the best significant (p < 0.05) values of digestion coefficient of dry matter ( 91.12%), ether extract ( 90.75% ), nitrogen free extract (71.64%), energy (76.67%), and resulted in significant lower (p < 0.05)values of crude protein digestion (81.14%), comparative to 32% protein level, while, a level of 27% crude protein improved significantly (p < 0.05) the digestion coefficient of dry matter (90.05%), ether extract (87.28%), nitrogen free extract (75.12%) and energy (75.19%) comparative to 32% dietary protein . 3-Within any dietary protein source, tested increasing the level of protein from 22 to 27 or 32% lowered significantly the digestion coefficient of dry matter, nitrogen free extract, energy and (p < 0.05) the digestion coefficient of ether extrad, while, the digestion of crude protein increased insignificantly. Fish fed on plant protein source at level of 22% showed higher insignificant value of digestion coefficient of dry matter ( 92.85% ),nitrogen free extract ( 75.74% ) and energy (77.54%), while, 22% protein level from animal plus plant protein source showed significantly the highest value (p < 0.05) of digestion coefficient of ether extract ( 92.88%) .