Impacts of Replacing Fish Meal With Duck By‐Product Meal in Diets on Growth Performance, Feed Utilization, and Economic Efficiency of Olive Flounder ( Paralichthys olivaceus )

Fish feeds are generally more expensive than livestock feeds because they contain high amounts of costly fish meal (FM). Therefore, formulating low‐FM diets is necessary for the sustainability of aquaculture. This study evaluates impacts of FM replacement with duck by‐product meal (DBM) in diets for olive flounder ( Paralichthys olivaceus ) on growth performance, feed utilization, and economic efficiency. Four hundred and fifty juvenile fish (initial weight of 6.30 g) were equally distributed into 18, 50‐L flow‐through tanks in triplicate. Six experimental diets were formulated to be isoproteic (52.0%) and isolipidic (12.0%). The control (Con) diet contained 60% FM. In the Con diet, 20%, 40%, 60%, 80%, and 100% of FM were substituted with DBM, named as the DBM20, DBM40, DBM60, DBM80, and DBM100 diets, respectively. Fish were hand‐fed to apparent satiation throughout the 50‐day trial. After the 50‐day feeding trial, weight gain (WG), specific growth rate, and feed consumption were significantly ( p < 0.0001 for all) higher in fish supplied with the Con, DBM20, and DBM40 diets than in those supplied with the DBM60, DBM80, and DBM100 diets. However, there were no significant ( p > 0.05) differences in feed utilization, plasma chemistry, and whole‐body fish supplied with the experimental diets. Amino acid and fatty acid profiles of the whole‐body fish were strongly influenced by dietary amino acid and fatty acid profiles. Economic profit index (EPI) of the Con, DBM20, and DBM40 diets was significantly ( p < 0.0001) higher than that of the DBM60, DBM80, and DBM100 diets. Therefore, DBM could replace up to 40% of FM in a 60% FM‐based diet without negative impacts on the growth performance, feed utilization, plasma chemistry, and chemical composition of olive flounder and EPI.