Evaluation of soy protein concentrate as a substitute for fishmeal in diets for juvenile starry flounder (Platichthys stellatus)

Fishmeal replacement with soy protein hydrolysate in diets for juvenile starry flounder (Platichthys stellatus) has been reported recently, but its application is limited due to high price and low yield. Whether it is feasible to replace dietary fishmeal protein (FMP) with cheap soy protein concentrate (SPC) for this fish remains uncertain. A feeding trialwas conducted to investigate the effect of diets containing SPC on growth performance, oxidation resistance, health status, feed digestion and nutritional composition of juvenile starry flounder. Six isonitrogenous and isolipidic diets were formulated with SPC to replace 0% (S0, control), 20% (S20), 40% (S40), 60% (S60), 80% (S80) and 100% (S100) of FMP. Each diet was randomly assigned to triplicate tanks with 80 fish (initial weight 12.76 +/- 0.2 g) per tank in a circulating water system. Fish were fed twice daily to apparent satiation for 10 weeks. At the end of the feeding trial, weight gain, specific growth rate, daily feed intake and survival rate were lower in fish fed diets S80 and S100 than in the other treatments. Feed efficiency ratio, protein efficiency ratio and condition factor were reduced by total FMP replacement (S100) compared to the control. The maximum FMP replacement for weight gain and protein efficiency ratio was estimated to be 54.86-59.02% using broken-line models. Moreover, serum lysozyme and superoxide dismutase activities decreased in fish fed diets S60, S80 and S100 versus S0, while aspartate aminotransferase, alanine transaminase and gamma-glutamyl transferase activities followed a reverse trend. Lower serum glutathione peroxidase corresponded to higher alkaline phosphatase activity in fish fed diets S80 and S100 versus S0. Serum total protein and albumin contents were reduced by total FMP replacement (S100), whereas cholesterol and low- and high-density lipoprotein cholesterol contents decreased with any diets containing SPC compared to S0. Pepsin and trypsin activities in the stomach, foregut and hindgut increased in fish fed S40 but decreased in fish fed S100. Amylase activity in the foregut was elevated by replacing at least 40% of FMP with SPC, while that in the hindgut increased with any diets containing SPC. Additionally, total FMP replacement reduced protein and fat contents but increased ash content of the whole fish compared to other treatments. These results indicated that SPC could be utilized effectively by juvenile starry flounder. FMP replacement with SPC by less than 40% is recommended for satisfactory fish growth and health. Statement of relevance Our work has proved that soy protein concentrate could be utilized effectively by juvenile starry flounder and less than 40% fishmeal could be replaced by soy protein concentrate with satisfactory fish growth and health. Present paper assesses the feasibility of replacement fishmeal with soy protein concentrate in diet for juvenile starry flounder. These results provided a basis for the formulation of a low-fishmeal diet in flatfish aquaculture. (C) 2015 Elsevier B.V. All rights reserved.