Effect of replacing dietary fish meal protein with combined animal meals on the growth performance of olive flounder (Paralichthys olivaceus)

The effect of various levels of fish meal (FM) protein substitution with combined animal meals on the growth and feed utilization of olive flounder (P. olivaceus) was elucidated. A total of 630 juvenile olive flounder averaging 12.5 g was distributed to 21 tanks, with 3 tanks per diet. A two-way ANOVA experimental design was adopted, incorporating two replacement sources [combined plasma powder and chicken by-product meal (PC), and combined plasma powder and tuna by-product meal (PT)] and three FM replacement ratios (25%, 50%, and 70%). A control (Con) diet contained 70% FM. In the Con diet, 25%, 50%, and 70% FM protein were substituted with PC and PT, labeled as the PC25, PC50, PC70, PT25, PT50, and PT70 diets, respectively. Fish were hand-fed to apparent satiation twice a day for 56 days. Upon completion of the feeding experiment, both dietary replacement source and ratio significantly affected the weight gain (WG), specific growth rate (SGR), and feed consumption of fish (P < 0.001 for all). The PT replacement source achieved better WG, SGR, and feed consumption than the PC replacement source. Additionally, dietary increased FM replacement ratio reduced WG, SGR, and feed consumption. WG, SGR, and feed consumption of fish fed the PC25 and PT25 diets were comparable to fish fed the Con diet, but superior to fish fed all other diets, except for feed consumption of fish fed the PT50 diet. None of proximate composition, AA profiles, plasma parameters as well as selected innate immunity (lysozyme and SOD activities) of fish was influenced by dietary treatments. In conclusion, up to 25% of FM protein (35.7% of FM replacement) in a 70% FM-based diet could be successfully substituted with PC and PT without negatively affecting growth, feed consumption and utilization, proximate composition, AA profiles, and selected innate immunity (lysozyme and SOD activities) of olive flounder.