Effect of adding neutral protease to diets on growth performance, digestion, and body composition of fingerling black carp (Mylopharyngodon piceus)
饲料中添加中性蛋白酶对青鱼生长、消化及鱼体组成的影响

A neutral protease product with an activity of 8000 u/g was used in the experiment. A basal diet without exogenous enzyme inclusion and four test diets adding 0. 5%0, 1%0, 2%0 and 3%0 of the enzyme product respectively were prepared to feed five triplicate groups of fish with an initial average body weight of (3.03 ± 0. 04) g. The feeding trial was conducted in 15 re circulating tank systems (80L each) at a controlled water temperature of 25 ± 0. 5℃ and lasted for eight weeks. At the end of eight weeks, the weight gain of fish fed a diet with 0. 5%0 of enzyme product showed no significant difference with that of fish fed basal diet (p ＞0. 05). When fish fed a diet with 1%0 of enzyme product, the weight gain increased significantly (p ＜ 0. 05) comparing with those of fish fed basal diet and the diet with 0. 5%0 of enzyme product, but higher levels of enzyme product inclusion seemed not to improve weight gain further. Fish fed diet with 1‰, 2‰ and 3‰ of enzyme product had higher feed ingest and lower feed conversion ratio than those of fish fed basal diet or the diet with 0. 5‰ of enzyme product (p ＜0. 05). There was no effect of adding the enzyme product in the diets on the apparent digestibility of dry matter, intestine protease activity, intestine and hepato-pancreas amylase activity, body composition, Viscera index, and Hepato-pancreas index (p ＞ 0. 05). However, the apparent digestibility of dietary protein of fish fed four test diets were significantly higher than that of fish fed the basal diet (p ＜ 0. 05). The hepato-pancreas protease activity increased with increasing dietary supplementing the enzyme product up to 1‰, but above this level, it appeared to keep stable. In conclusion, under the condition of this experiment, adding 1‰ -3‰ neutral protease product to fingerling black carp diet could promote feed ingest and digest capacity of dietary protein, and as a result, improve fish growth and feed conversion.