A feeding trial was conducted for 75 d to evaluate the nutritive value of a mixture of animal by-products (MAB) as a possible protein source in diets for juvenile mangrove red snapper, Lutjanus argentimaculatus (mean initial body weight, 30 g). Fish were fed one of five isonitrogenous diets (40% crude protein) replacing 0, 25% (MAB25), 50% (MAB50), 75% (MAB75) and 100% (MAB100) of fish meal protein with similar percentages of MAB. The MAB consisted of 25% cow liver meal, 20% leather meal, 20% meat and bone meal, 15% blood meal, 10% APC (poultry feather meal), 8% poultry manure dried, 1.5% choline and 0.5% chromic oxide. After 75 d of feeding, fish fed with diets MAB50, MAB75 and MAB100 exhibited significantly lower growth performance than that of fish fed with control and MAB25 diets. The optimum level of MAB was estimated to be 23%. Replacement of fish meal by MAB23% showed the following performance: maximum weight gain, 510%; SGR, 2.39% and FCE, 2.83%. The MAB substitution up to 75% of fish meal protein in diets did not show differences in apparent protein digestibility (83.6% for MAB25, 79.2% for MAB50, 78.7% for MAB75) compared with control (83.4%), whereas in MAB100 group digestibility (65.3%) was significantly lower than in other groups. The apparent phosphorus absorption of test diet groups was significantly higher (37.1% for MAB25, 28.5% for MAB50, 55.6% for MAB75 and 54.5% for MAB100) than that of control (11.2%). The levels of protein and ash in the whole body, carcass and viscera increased as MAB substitution in diets increased, whereas lipids and moisture remained consistent among all treatment groups. These results showed that approximately 23% of fish meal protein could be replaced by a mixture of animal by-products for juvenile snapper growing from 30 g to 167 g in 75 d without compromising growth performance and feed efficiency.

A feeding trial was conducted in a recirculating water system to investigate the effects of dietary protein levels on growth, feed utilization, hepatosomatic index and liver lipid deposition of juvenile red snapper, Lutjanus argentimaculatus (average initial wet weight 8.0--0.39 g and total length 3.14 _+ 0.3 cm). In the experiment, six fishmeal-based diets were formulated to contain various protein levels (20% to 45% in 5% increments), with dietary energy ranging from 2 210.7 kJ 100 g to 2 250.2 kJ 100 g dry matter. The protein to energy ratios of diets ranged from 8.58 mgproteinkJ -1 to 20.03 mgprotein kJ < . Diets were fed for 90d to triplicate groups of fish stocked in 0.128 m 3 seawater tanks, 25 individuals each. The daily ration of 2% wet body weight was offered to the fish thrice a day. The fish at the end of the study had more than ten-fold (77.0 g) increase in weight compared to the initial (8.0 g). Fish fed diets of 40% and 45% protein produced significantly (P < 0.05) higher weight gain of 77.2 g and 76.5 g, and specific growth rate (SGR) of 2.65% and 2.62% than those of 67.0 g and 68.3 g, and 2.49% and 2.51% of the other diets. The broken-line regression of SGR against dietary protein level yielded an optimum dietary protein requirement of 42.6% ( Y = -1.6295 + 0.1114 X 2, P < 0.05). Survival remained 100% among groups. Feed conversion ratio decreased from 0.45 for fish fed 20% dietary protein to 0.35 for fish fed 45% dietary protein. Nitrogen intake increased with an increase in dietary protein, which in turn resulted in an increase in nitrogen gain of fish whole body. Fish fed 40% and 45 % protein diets showed higher (P < 0.05) nitrogen gain (0.27 g and 0.26 g) than those (0.23 g and 025 g) fed all other diets. Gross energy intake (GEl) in fish fed 45% protein was lower (600.67 kJ) than that (607.97 kJ) of 40% protein diet, though the differences were not statistically significant (P >0.05); GEl ranging from 677.31 kJ to 663.20 kJ at remaining four diets (20% to 35% protein) did not appear to differ significantly (P > 0.05). The highest energy gain of 518.33 kJ was obtained with fish fed 40% protein, resulting in the highest energy retention efficiency of 85.26%. The hepatosomatic index of fish fed diets of 20%, 25%, 30% and 35% protein were significantly (P< 0.05) higher (2.09% to 2.57%) than those (1.44% and 1.41%) of fish fed diets containing 40% and 45% protein. Liver lipid contents decreased from 8.72% to 7.0% in fish fed dietary protein of 20% to 45% in 5% increments. Results suggest that the diet containing 40% to 42.6% protein with a P/E ratio of 17.6 mg protein kJ -1 is required for good growth of L. argentimaculatus weighing between 8.0 g and 85.2 g under the culture conditions of the present study.