Evaluation of Clostridium autoethanogenum protein as a fish meal substitute in diets for juvenile mud crab (Scylla paramamosain)

A nine-week feeding trial was conducted to assessed the impacts of replacing fish meal (FM) with Clostridium autoethanogenum protein (CAP) on the growth performance, amino acid profiles, digestive enzyme activities, antioxidant capacity, immune response, and protein metabolism of juvenile mud crab (Scylla paramamosain). Total of 150 crabs were divided into 5 groups and fed the experimental diets with replacing FM levels of 0 %, 15 %, 30 %, 45 %, and 60 % with CAP, respectively. Crabs fed the CAP15 diet exhibited significantly higher PWG and SGR than crabs fed the CAP60 diet, moreover, survival exceeded 70 % in all groups, with no significant differences observed among treatments. The amino acid profile in muscle and hepatopancreas of crabs were significantly affected by replacement of FM with CAP. The concentrations of T-CHO, ALT, AST and blood ammonia in serum, and TG in hepatopancreas, increased significantly with higher CAP inclusion. Crabs fed the CAP15 and CAP30 diet exhibited higher activities of T-AOC in serum and T-SOD, GSH, ACP and AKP in hepatopancreas compared with control diet. Digestive enzyme activities in hepatopancreas were highest in crabs fed the CAP15 diet. Furthermore, the expression of prx and gpx in hepatopancreas, and prx, trx, cat, and tgf in intestine were significantly up-regulated in crabs fed CAP15 and CAP30 diets. Key genes associated with protein metabolism were significantly up-regulated with the replacement levels of FM with CAP increasing from 0 % to 30 %. Thus, the optimal replacement level of FM with CAP was estimated to be 16.52 % for juvenile mud crab based on broken-line regression analysis.