Effects of exogenous enzyme supplementation in diets on growth and feed utilization in tilapia, Oreochromis niloticus x O-aureus

A 12-week feeding trial was conducted to investigate the effects of supplemental exogenous enzyme on growth performance in juvenile hybrid tilapia Oreochromis niloticus x O. aureus (18 g, average initial weight). A commercial enzyme complex (neutral protease, beta-glucanase and xylanase) was included at the level of 0.0 (control group), 1.0 and 1.5 g kg(-1) diet in three test diets. Each diet was fed to triplicate tanks of the juvenile three times a day at 4-6% of wet body weight, and each tank was stocked with 50 fish. The results showed that specific growth rate and feed efficiency ratio significantly increased (P < 0.05) with increasing dietary enzyme levels. The highest feed intake was recorded in the group fed the control diet (P < 0.05). The highest apparent protein retention was observed in fish fed the diet containing the 1.5 g kg(-1)diet (P < 0.05). No significant differences were observed in the apparent digestibilities (ADC) of protein, lipid and gross energy among dietary treatments (P > 0.05). However, the ADC of dry matter in fish fed high supplementation (1.5 g kg(-1)) was significantly higher than the control and low supplementation (P < 0.05). There were no significant differences in condition factor, whole body moisture, protein, lipid and ash among dietary treatments. Viscera ratio, hepatosomatic index and the liver lipid decreased significantly with increasing enzyme (P < 0.05). Both protease and amylase activities in the intestine and the hepatopancreas of juvenile hybrid tilapia significantly increased (P < 0.05) with increasing dietary enzyme levels. The results suggested that enzyme supplementation can significantly improve growth performance and feed utilization in juvenile hybrid tilapia.