Animal and plant proteins as alternative ingredients in diets for sub-adult olive flounder Paralichthys olivaceus at farm conditions

A 20-week feeding trial was performed to evaluate the optimum level of animal and plant protein sources as substitutes of fishmeal (FM) in the diets of sub-adult olive flounder (Paralichthys olivaceus) under farmed conditions. Groups of ninety fish averaging 478 +/- 4.7 g (mean +/- SD) were randomly distributed into four treatments in triplicates. An FM-based diet was used as control (CON) and three other diets replaced 20% (APP(20)), 30% (APP(30)) and 40% (APP(40)) of FM with animal (tankage meal and poultry by-product meal) and plant (soy protein concentrate) protein sources. Weight gain, specific growth rate and protein efficiency ratio were not significantly different among fish fed all the experimental diets (p > 0.05). The feed efficiency of fish fed the APP(40) diet was significantly lower than those of fish fed the other experimental diets (p < 0.05). Non-specific immune responses such as superoxide dismutase activity and lysozyme activity of fish fed all the experimental diets were not significantly different (p > 0.05). Intestinal villi length of fish fed the CON diet was significantly higher than those of fish fed the other diets (p < 0.05). Based on the results of growth performances and the non-specific immune responses, the dietary combination of animal and plant protein sources could replace up to 40% of FM in sub-adult olive flounder.