Document Type : Primary Research paper
A 56–day 3 x 3 factorial experiment was conducted to evaluate the effects of three levels of dietary crude protein (40, 45, and 50%) and three levels of crude fat (8, 12, and 16%) on the performance of Cynoscion othonopterus juveniles (initial mean body weight of 102.6±14.1 g). The levels of dietary crude protein and fat tested, or their interaction, did not influence significantly the growth response, as evaluated by final weight, weight gain, percent weight gain, thermal growth coefficient, feed conversion ratio, or survival. Apparent digestibility coefficients of dry matter of experimental feeds ranged from 74.1 to 80.2%, without significant differences among treatments. In muscle tissue, increased crude fat deposition was observed in response to increasing levels of this nutrient. However, the content of crude protein and ash decreased significantly with both dietary crude protein and fat. In turn, moisture content increased significantly with dietary crude protein, from 71.2±2.5% (at 40% crude protein), to 75.9±1.4% (at 50% crude protein), but it was not affected by dietary crude fat. It appeared that 40% dietary crude protein was sufficient to promote adequate growth and survival for this species. Further research is warranted to evaluate if dietary protein requirements of C. othonopterus are below 40%, and to further elucidate the extent of the observed protein-sparing effect of dietary lipid.