Evaluation of solid-state fermented protein concentrates as a fish meal replacer in the diets of juvenile rainbow trout, Oncorhynchus mykiss

We evaluated four fermented protein concentrates (FPCs) as a fish meal replacer in juvenile rainbow trout, Oncorhynchus mykiss. Ten diets were formulated to contain low-temperature fish meal (LT-FM), Vietnam fish meal (VT-FM) and four types of FPCs as fish meal replacers (FPC-A, B, C & D) at 30% and 50% FM replacement levels. FPC-A was a mixture of solid-state fermented soybean meal (SBM) and corn gluten meal (CGM) with Bacillus subtilis; FPC-B was pretreated acid-hydrolysed FPC-A; FPC-C and FPC-D were FPC-A + 2% shrimp soluble extract (SSE) and FPC-B + 2% SSE, respectively. Triplicate groups of fish (average 15.4 g) were fed one of the experimental diets for 8 weeks. At the end of the feeding trial, fish fed the LT-FM, FPC-B, FPC-C and FPC-D diets showed significantly higher growth performance at 30% FM replacement than those of fish fed the FPC diets at 50% FM replacement. Fish fed 30FPC-B, 30FPC-C and 30FPC-D diets showed higher weight gain (WG) than fish fed 30FPC-A diet. Haematological parameters showed no clear trends among the experimental groups. Superoxide dismutase, lysozyme and myeloperoxidase activities were found to be higher in fish fed the LT-FM, FPC-A, FPC-B, FPC-C and FPC-D diets at 30% FM replacement than in fish fed the FPC diets at 50% FM replacement. Antinutritional factors such as α- and β-conglycinin, glycinin, trypsin inhibitors or zein were absent in FPC compared with SBM and CGM. Intestinal villi length and muscular thickness were significantly reduced in fish fed the VT-FM and FPC diets at 50% FM replacement compared to fish fed the LT-FM and FPC diets at 30% FM replacement. The results show that FPC-B, FPC-C, FPC-D could replace up to 30% of LT-FM in juvenile rainbow trout.