The effects of different levels of dietary fermented plant-based protein concentrate on growth, hematology and non-specific immune responses in juvenile olive flounder, Paralichthys olivaceus

An 8-week feeding trial was conducted to investigate the effects of dietary level of fermented plant-based protein concentrate (FPPC) as a fish meal (FM) replacer on growth, hematology, and non-specific immune responses in juvenile olive flounder. Soybean meal and corn gluten meal pre-treated by acid hydrolysis were mixed by the ratio 1:1, and the mixtures were fermented by Bacillus subtilis at 37 °C and 95% humidity to produce FPPC. Triplicated groups of 20 fish weighing 8.36 ± 0.02 g (mean ± SD) were fed one of the six experimental diets formulated to replace FM with FPPC at 0%, 7.5%, 15%, 22.5%, 30%, and 40% (CON, FPPC7.5, FPPC15, FPPC 22.5, FPPC30, and FPPC40, respectively). Five FPPC diets were supplemented with lysine and methionine to balance amino acids levels as the control diet. After the feeding trial, weight gain, feed efficiency, and specific growth rate of fish fed the FPPC40 diet were significantly lower than those of fish fed the other diets (P < 0.05), whereas no significant difference was detected in those measurements of fish fed the CON, FPPC7.5, FPPC15, FPPC22.5, and FPPC30 diets (P ≥ 0.05). Survival rate, whole-body proximate composition, hematological parameters (aspartate amino transferase, alanine amino transferase, glucose, and total protein in serum), and non-specific immune responses (lysozyme and superoxide dismutase activity) were not significantly influenced by the inclusion of the graded FPPC in the flounder diet. Based on the overall responses and the two-slope broken-line regression analysis on feed efficiency, FM can be replaced with the FPPC up to 27.9% of FM in the flounder diet.