Fish Meal Substitution Effects with the Combined Animal Proteins in the Feeds of Olive Flounder on Growth Performance, Feed Availability, and Disease Resistance against IStreptococcus iniae/I

As fish meal (FM) has become an unsustainable natural resource in fish feeds because of its plateaued production and increased price, looking for a substitute for FM is a tremendous concern for scientists. Meat meal (MM) and chicken by-product meal (CBM) are known as suitable replacers for FM in the olive flounder (P. olivaceus) feeds. The combined proteins can substitute for more FM than each of the respective protein sources in diets because the former can compensate for their nutritional deficiency or imbalance. However, FM substitution with an alternative source in fish feeds may influence the immunity of fish. Therefore, this study evaluated the FM replacement effect of the combined MM and CBM (CMC) in the olive flounder feeds on growth, feed availability, and disease resistance against S. iniae. The results of this study indicated that FM up to 60% (39% FM protein in the diet) could be replaceable with CMC in the 65% FM-based diets of olive flounder without causing an unfavorable effect on growth performance, feed availability, or survival of fish after S. iniae infection. This study aims to reveal the substitution impact of fish meal (FM) with the combined meat meal and chicken by-product meal (CMC) in the olive flounder (P. olivaceus) feeds on growth and feed availability. Seven experimental feeds were formulated. The control (CMC0) diet included 65% FM. In the CMC0 diet, the various (10%, 20%, 40%, 60%, 80%, and 100%) levels of FM were replaced with CMC, named as the CMC10, CMC20, CMC40, CMC60, CMC80, and CMC100 diets, respectively. The total number of 525 juvenile fish (9.2 ± 0.01 g; mean ± SD) was placed into 21 50-L flow-through tanks (25 juveniles/tank) with three replicates. Fish were hand-fed to apparent satiation for 8 weeks. After the 8-week feeding experiment, olive flounder fed the CMC10 (40.0 ± 0.60 g/fish, 2.99 ± 0.021%/day, and 39.57 ± 0.542 g/fish; mean ± SD), CMC20 (47.3 ± 2.58 g/fish, 3.24 ± 0.082%/day, and 45.16 ± 0.760 g/fish), and CMC40 (40.2 ± 1.17 g/fish, 3.00 ± 0.040%/day, and 39.43 ± 0.930 g/fish) diets attained superior (p < 0.0001 for all) weight gain, specific growth rate (SGR), and feed consumption compared to olive flounder fed the CMC0 (35.1 ± 0.96 g/fish, 2.81 ± 0.039%/day, and 33.75 ± 0.544 g/fish), CMC60 (31.7 ± 1.62 g/fish, 2.66 ± 0.068%/day, and 31.60 ± 1.080 g/fish), CMC80 (24.7 ± 0.63 g/fish, 2.33 ± 0.033%/day, and 25.27 ± 0.689 g/fish), and CMC100 (17.8 ± 0.32 g/fish, 1.92 ± 0.021%/day, and 18.99 ± 0.592 g/fish