Plant protein ingredients with lysine supplementation reduce dietary protein level in rainbow trout (Oncorhynchus mykiss) diets, and reduce ammonia nitrogen and soluble phosphorus excretion

Two experiments were conducted to evaluate the effects of lysine supplementation on the reduction of dietary crude protein (CP), and reductions of total ammonia nitrogen (TAN) and soluble phosphorus (soluble-P) discharged into water by rainbow trout. In Experiment 1, eight diets were prepared, such that Diet 1 contained 32.8% fish meal, 42% CP and 2.1% lysine. Diet 2 had the same amount of fish meal and lysine as in Diet 1, but only 37% CP. Diets 3-8 contained 16.4% fish meal, 37% CP, and 1.5%, 1.65%, 1.8%, 1.95%, 2.1%, and 2.25% lysine, respectively. Rainbow trout (initial body weight: 26.9 +/- 0.2 g) were randomly assigned to triplicate tanks per diet with 50 fish per tank. After an 8-week feeding trial, weight gains were 112.5, 111.8, 87.5, 94.4, 103.0, 105.7, 101.8, and 102.6 g; feed conversion ratios were 0.99, 1.01, 1.16, 1.15, 1.10, 1.08, 1.10, and 1.09 g feed/g gain for fish fed diets 1-8, respectively. Survival was greater than 99% for all treatments. In Experiment 2, 130 fish (102.4 +/- 8.3 g) per tank were moved to flowing water tanks (140 1) and fed the same diets as in Experiment 1 for 1 week, and then TAN and soluble-P in the wastewater were measured for 2 consecutive days. The values of TAN discharged by the fish 8 h after feeding were 9.69, 8.56, 8.44, 7.81, 7.19, 6.65, 6.24, and 6.29 mg/l, and discharged soluble-P were 1.01, 0.85, 0.45, 0.31, 0.30, 0.26, 0.25, and 0.14 mg/l for fish fed Diets 1-8, respectively. Results showed that lysine supplementation in plant protein-based diets allowed dietary CP to be reduced without reducing fish performance. TAN and soluble-P excretions by rainbow trout were reduced in plant protein-based diets (37% CP) with lysine supplementation compared to the control fish fed with fish meal diets with either 42% or 37% CP. (C) 2003 Elsevier Science B.V. All rights reserved.