Non‐fish meal,non‐fish oil diet development for red sea bream,Pagrus major,with plant protein and graded levels of Schizochytrium sp.: Effect on growth and fatty acid composition

A feeding experiment was conducted to determine the optimal formulation level of algae meal, which is rich in docosahexaenoic acid (DHA), in a non‐fish meal diet. Six iso‐nitrogenous (450 g/kg) and iso‐lipidic (130 g/kg) experimental diets were prepared. The control diet was formulated with fish meal (400 g/kg), fish oil (60 g/kg), plant protein sources (220 g/kg) and rapeseed oil (50 g/kg). Plant protein sources (soy protein concentrate, soybean meal and corn gluten meal), rapeseed and fish oil were formulated in the second diet (NFM + FO). In the third diet, fish oil of the NFM + FO diet was replaced by rapeseed oil (NFM + NFO) and designated as the negative control. In the other three diets, rapeseed oil in the NFM + NFO diet was replaced with algae meal (Schizochytrium sp. powder) at 50 g/kg, 100 g/kg and 150 g/kg (AM5, AM10 and AM15, respectively). Triplicate groups of juvenile red sea bream (8.8 g) were fed the experimental diets for 12 weeks near satiation. The growth was lowest in the fish fed NFM + NFO diet. This was improved by the formulation of algae meal, which reached the growth level of the NFM + FO group in the AM10 group. The lipid content of the whole fish body in the NFM + NFO group was significantly lower than those of other groups. The fatty acid profile showed significant differences among dietary treatments. DHA content in total and polar lipids of the whole body and liver was highest in the AM10 and AM15 groups. These results reconfirm that microalgae are a suitable lipid source for the replacement of dietary fish oil for marine fish, and the optimal level was estimated as 50 g/kg?100 g/kg in diet.