Abstract
Antimicrobial peptides (AMPs) are small-molecule polypeptides with broad-spectrum antibacterial and immunomodulatory properties. As feed additives, they have demonstrated synergistic effects in aquaculture by enhancing growth performance and maintaining host health. Its negligible drug resistance makes it an ideal additive to replace antibiotics in the "antibiotic-free breeding" system. Antimicrobial peptides were added to the basic diet of the crucian carp (Carassius auratus) to assess their impacts on growth, muscle quality, antioxidant capacity, immune function, and key gene expression in the TLR4/NF-κB signaling pathway. Crucian carp were fed with experimental diets containing antimicrobial peptides for 49 days, namely four treatments: L0 (0 g/kg), L1 (0.2 g/kg), L2 (0.4 g/kg), and L3 (0.6 g/kg), with three repetitions of each treatment. The findings indicated that AMPs had the potential to improve growth performance and muscle quality. The final weight, WGR, and SGR of crucian carp of group L1 significantly increased compared with groups L0 and L3 (p < 0.05). The condition factor of group L2 significantly increased compared with group L0 (p < 0.05). The FCR of groups L0, L1, and L2 was significantly reduced compared with group L3 (p < 0.05). The muscle redness of group L1 was significantly higher compared with groups L0, L2, and L3 (p < 0.05). The muscle shear force of groups L0, L1, and L2 was significantly lower compared with group L3 (p < 0.05). The crude protein content of groups L0, L1, and L2 showed significantly higher crude protein content than group L3 (p < 0.05). Conversely, the crude fat content was significantly lower in groups L1, L2, and L3 compared with group L0 (p < 0.05). The superoxide dismutase (SOD) activity of group L1 was significantly higher compared with groups L0, L2, and L3 (p < 0.05). The catalase (CAT) activity of groups L0 and L1 was significantly increased compared with groups L2 and L3 (p < 0.05). The malondialdehyde (MDA) content of groups L1 and L2 was significantly reduced compared with groups L0 and L3 (p < 0.05). The acid phosphatase (ACP) activity of groups L1 and L2 was significantly increased compared with group L0 (p < 0.05). The alkaline phosphatase (AKP) activity of group L1 was significantly increased compared with groups L0 and L3 (p < 0.05). Compared with groups L2 and L3, the lysozyme activity of group L1 was significantly increased (p < 0.05). The C3 content of groups L1, L2, and L3 was significantly higher compared with group L0 (p < 0.05). Similarly, C4 levels of groups L2 and L3 significantly exceeded group L0 (p < 0.05). For inflammatory cytokines, the IL-1 levels of groups L1 and L2 were significantly higher than those of group L0 (p < 0.05). The IL-6 and IL-12 levels of groups L0, L1, and L2 significantly increased compared with group L3 (p < 0.05). Compared with group L0, the levels of TNF and IFN-γ of groups L1, L2, and L3 were significantly higher (p < 0.05). Compared with group L0, the relative expression levels and protein expression levels of key genes TLR4, MyD88, IRAK4, TRAF6, and NF-κB of groups L1, L2, and L3 were significantly upregulated (p < 0.05). In conclusion, supplementation with 0.2-0.4 g/kg antimicrobial peptides promoted the growth of crucian carp, improved muscle quality, enhanced the antioxidant capacity, and boosted immunity through modulation of the TLR4/NF-κB signaling pathway.