Evaluating the efficacy of partially substituting fish meal with unfermented tuna by-product meal in diets on the growth, feed utilization, chemical composition and non-specific immune responses of olive flounder (Paralichthys olivaceus)

Fish meal (FM) usage in aquafeed is fraught with cost and environmental challenges. Alternatives to FM must be readily available and with adequate protein. This 8-weeks study explored the utilization of tuna by-product meal (TBM) without fermentation as a substitute for FM in diet on growth, feed utilization, chemical composition, plasma chemistry, and non-immune responses of olive flounder (Paralichthys olivaceus). Four hundred juveniles (initial weight of 14.7 g) were randomly distributed to 20 tanks (20 fish per tank). The control (Con) diet contained 65% FM without replacement, and in the TBM10, TBM20, TBM30, TBM40, and TBM50 diets, FM was substituted with 10%, 20%, 30%, 40%, and 50% TBM, respectively. Each diet was fed to triplicate groups of fish, but quadruplicate groups for the Con and TBM30 diets. Survival was not different among the experimental diets. Superior weight gain, specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio were observed in fish fed the TBM40 and TBM50 diets to fish fed all other diets. Condition factor of fish fed the TBM40 and TBM50 diets was higher than that of fish fed the Con diet. Feed consumption, chemical composition, and amino acid profiles of the whole body fish, except for the tryptophan content, viscerosomatic and hepatosomatic indices, plasma biochemical parameters, non-specific immune responses were not affected by the experimental diets. In conclusion, FM up to 50% can be replaced with TBM without impairing growth, feed utilization, nutritional composition, plasma chemistry, and non-specific immune responses of olive flounder when 65% FM was included. The greatest weight gain, SGR, and FER of fish were estimated to be 47.1%, 48.6%, and 46.3% of dietary substitution of FM with TBM, respectively.