| Summary: | This study evaluated the effect of replacing dietary fish meal with poultry by-product meal (PBM), cottonseed-protein concentrate (CPC) and their blend on growth, feed utilization, body composition, waste outputs and carbon-nitrogen-phosphorus atomic stoichiometry in wastes of largemouth bass, Micropterus salmoides. A diet containing 40 % fish meal served as reference (RF), and 60 % and 80 % of the fish meal was replaced by PBM (P60 and P80) and CPC (C60, C80) alone or in combination (CP60 and CP80). Moreover, a cost-effective diet (CPS80) was formulated by replacing 80 % of the fish meal with a blend of PBM, CPC and soybean meal. Largemouth bass weighing 24.0 ± 0.3 g were fed the test diets for eight weeks. Weight gain, retention efficiencies of nitrogen and phosphorus were lower, while wastes of carbon, nitrogen and phosphorus were higher, in fish fed diet RF than in fish fed diets P60, P80, C60, C80, CP60, CP80 and CPS80, and no significant differences were found in condition factor and hepatosomatic index between fish fed diet RF and the low fish meal diets. At the same fish meal replacement level, weight gain was slightly high in fish fed diets P60, P80, CP60 and CP80, relative to fish fed diets C60 and C80. Fish fed diets CP80 and CPS80 exhibited high weight gain and minimum feed cost, fish meal reliance and waste outputs. Carbon-nitrogen-phosphorus atomic stoichiometry in wastes was (50–86):(10–17):1, and C : P and N : P in wastes of fish fed diet CPS80 were high relative to that of fish fed diet RF and diets C60, C80, P60, P80, CP60 and CP80. This study indicates that dietary fish meal level for largemouth bass could be reduced to 80 g/kg by using PBM and CPC in combination as a fish meal substitute, and feeding diet CP80 and CPS80 can significantly reduce feed cost and fish meal reliance without increasing negative effect on growth and environment.
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