Effects of Replacing Dietary Fish Meal by Soybean Meal Co-Fermented Using Bacillus subtilis and Enterococcus faecium on Serum Antioxidant Indices and Gut Microbiota of Crucian Carp Carassius auratus

Fermented soybean meal (FSM) is an important feed material that can replace fish to solve the shortage of animal protein. To improve utilization FSM, we optimized co-fermentation conditions using Bacillus subtilis and Enterococcus faecium studied effects replacing with different proportions FSM on serum antioxidant indices gut microbiota (GM) composition crucian carp (Carassius auratus). Our results showed was most effective when ratio B. X-2 E. X-4 2:3, glucose addition 4.5%, KH2PO4 0.15%, MgSO4·7H2O 0.1%, anhydrous sodium acetate 0.4%, fermentation time 120 h, solid–water 1:1. Replacing 40% in significantly improved T-AOC, POD, IgM levels C. auratus. Although there were significant differences midgut hindgut structures auratus, did not cause GM structure, whether or hindgut. Therefore, suitable substitute for