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Feeds for carnivorous fish contain large proportions of fish meal. Increasing amounts of plant protein meals must be formulated into fish feeds since fish meal production is not growing worldwide. However, relative to fish meal, many plant protein meals are deficient in lysine. In this experiment, seven diets were made such that the reference diet (Diet 1) contained 32.1% fish meal, 46% crude protein (CP) and 2.25% lysine. The basal diet (Diet 2) had 15% fish meal, 43% CP and 1.5% lysine. Diets 3–7 contained 15% fish meal, 43% CP and 1.65, 1.8, 1.95, 2.1 and 2.25% lysine, respectively. Diets 2–7 were isonitrogenous and all diets were isocaloric. One thousand and fifty rainbow trout (initial body weight 14.9±0.4 g) were randomly assigned to twenty-one 150-l fiberglass tanks with 50 fish per tank, and three tanks per dietary treatment. After an 8-week growth period, weight gains were 82.7, 57.9, 61.7, 73.2, 74.5, 72.8, 71.8 g for fish fed Diets 1–7, respectively. Feed conversion ratios were 0.99, 1.18, 1.18, 1.08, 1.09, 1.07 and 1.08 g feed/g gain for fish fed Diets 1–7, respectively. Results showed that more than 50% fish meal in rainbow trout diets could be replaced by plant protein meals without significantly reducing fish growth and increasing feed conversion ratio if these diets were supplemented with 0.4% or higher levels of lysine. Furthermore, lysine supplementation increased CP and lysine, and reduced fat levels in whole trout body (P 88%) in all diets, ADCs of dry matter were in the range of 72.0–75.6%, and ADCs of phosphorus varied from 47.7% to 61.8%. |
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