Effects of Four Vegetable Protein Supplementation on Growth, Digestive Enzyme Activities, and Liver Functions of Juvenile Tilapia, Oreochromis niloticusxOreochromis aureus

Four isonitrogenous (gross protein content 30%) and isoenergetic (gross energy content 15 kJ/g) diets were formulated to investigate the effects of inclusion of plant proteins on the hybrid tilapia (Oreochromis niloticusxOreochromis aureus). The plant proteins tested were soybean meal (SBM), rapeseed meal (RSM), cottonseed meal (CSM), and peanut meal (PNM). In each diet, 30% of the protein was supplied by fish meal, and the rest of protein was supplied by the plant protein tested. Each diet was randomly fed to three groups of hybrid tilapia for 8 wk in a recirculating freshwater system. The results showed that the best performance in terms of final weight, specific growth rate, feed efficiency ratio, and protein efficiency ratio were shown in diets SBM and CSM. Four parameters were significantly affected by dietary RSM (P < 0.05). The lowest feed intake was recorded in the group fed RSM, followed by groups CSM and SBM, and was highest in the group fed PNM. Whole-body moisture content in group PNM was significantly lower than that of other three groups (P < 0.05). The liver lipid content in group RSM was significantly higher than that of other three groups (P < 0.05). And viscera ratio, hepatosomatic index, condition factor, and the liver glycogen contents were not significantly different among ditary treatments (P < 0.05). Protease activities of intestine in diets SBM and CSM are significantly higher than that of other two groups (P < 0.05), and the lowest protease activities of intestine and hepatopancreas were found in group RSM. No significant differences were observed in amylase activities of intestine and hepatopancreas among four diet groups (P > 0.05). The highest activities of glutamate-pyruvate transaminase, glutamate-oxaloacetate transaminase, and superoxide dismutase in the liver were observed in group SBM and the poorest in group RSM. The results show that 39% CSM may be included in the practical diets without inhibiting fish performance. Although the inclusion of 50% RSM resulted in significantly lower growth performance, it produced histopathological damage in the liver.