Effect of reducing ۳.۲% dietary protein level on the growth performance and immunity of Nile tilapia (Oreochromis niloticus) with supplementation of multi amino acids

Reducing dietary protein content in fish feeds will reduce cost of production if growth performance can be maintained. In this study, we assessed the effects of reduced dietary protein content from ۳۳.۵% to ۲۷.۴% with ideal amino acids profile on the growth, immune parameters, intestinal microvilli length and total ammonia nitrogen discharge of tilapia. After ۸ weeks of feeding, growth performance and feed efficiency were not affected by reducing dietary protein content from ۳۳.۵% to ۳۰.۳%, while fish fed ۲۷.۴% CP had the lowest weight gain. Total ammonia nitrogen discharged into the water ۹ hours after the feeding was decreased by about ۳۵%. Serum lysozyme activity, blood respiratory burst activity and serum ACH۵۰ were not significantly affected by dietary protein content. Fold height, enterocyte height and microvillus height of proximal and middle intestine were significantly increased with reducing of dietary protein. Results indicated that ۳.۲% dietary protein content can be reduced, which had no effects on growth performance and immunity of Nile tilapia in practical diet.