Effects of replacing fish meal with rendered animal protein and plant protein sources on growth response, biological indices, and amino acid availability for rainbow trout Oncorhynchus mykiss

Duplicate groups of rainbow trout (mean initial weight 16.7 +/- A 0.1 g) were fed six isonitrogenous (43.7 % crude protein) diets for 12 weeks. A fish-meal-based diet was designated the control. In the other five diets, 75 or 100 % of the fish meal was replaced with either poultry by-product meal (PBM), hydrolyzed feather meal (FEM), and spray-dried blood meal (BM) or with defatted soybean meal and corn gluten meal. Trout fed the diets in which 75 and 100 % of the fish meal was replaced with rendered animal protein showed comparable growth performance to trout fed the control diet except in terms of the protein efficiency ratio and feed conversion ratio. The feed intake of the trout fed a combination of fish meal and rendered animal protein (either with or without plant protein) was significantly higher than the feed intake of trout on the fish-meal-based diet. Apparent crude protein digestibility coefficients were significantly higher in trout fed the diets in which 75 % of the fish meal was replaced with plant protein sources than in trout fed the diets in which 75 % of the fish meal was replaced with rendered animal protein sources (P < 0.05). These results suggest that a combination of PBM, FEM, and BM is a good substitute for most of the fish meal in practical feed for rainbow trout.