Effects of fermented Clitocybe maxima stalk waste and soybean meal mixture on growth, serum biochemistry, and gut health in juvenile Larimichthys crocea

A 56-day feeding trial was carried out to compare the effects of big clitocybe (Clitocybe maxima) stalk waste and soybean meal (SBM) mixture fermented by microorganisms alone (BFBS) or in combination with enzymes (EBFBS) on growth performance, serum biochemistry, and gut health in large yellow croaker (Larimichthys crocea). Fermented ingredients (BFBS and EBFBS) were included at 10 % in the diet, replacing SBM. Large yellow croaker was randomly assigned to three groups (control, BFPS, and EBFPS) with four replicates per group. Results showed that BFBS and EBFBS improved growth performance, feed utilization, and organ-somatic indices. Dietary BFBS and EBFBS significantly elevated serum alkaline phosphatase and acid phosphatase activities, and reduced serum aspartate transaminase and alanine transferase activities, IL-1β and TGF-β1 contents, indicating systemic immune stimulation and inflammation inhibition in croakers. Dietary BFBS and EBFBS decreased serum D-lactate content and diamine oxidase activities, in parallel with the enhancements of muscle thickness, villus height, and expressions of zo-1 and claudin-11 mRNA. Moreover, BFBS and EBFBS moderately activated intestinal inflammation and inhibited TLRs signaling, showing up-regulation of pro-inflammatory il-1β and il-6 and down-regulation of tlr1, tlr2b, and anti-inflammatory il-4/13a, il-10, and tgf-β1. BFBS and EBFBS increased diversities of gut microbiota; meanwhile, the enhancement of Firmicutes (only in BFBS group) and the reduction of Proteobacteria (only in BFBS group) and Brevinema were observed in BFBS and EBFBS groups, suggesting that fermented feedstuffs could positively shape the gut microbiota. In conclusion, BFBS and EBFBS have excellent potential in improving growth, immunity, and intestinal health of large yellow croaker (L. crocea). It is worth noting that EBFBS, in particular, showed superior performance in these aspects compared to BFBS, indicating that enzyme-assisted bacterial fermentation may be a more effective approach for ingredient fermentation. The work will provide a novel insight into the development of effective protein sources for aquafeeds and high-value utilization of residual wastes in the mushrooms processing chain.