Effects of different dietary zinc sources on growth performance, muscle texture, and intestinal immunity in Mandarin Fish (Siniperca chuatsi)

The study aims to examine the effects of different dietary zinc sources on growth performance, muscle texture, and intestinal immunity in Mandarin Fish (Siniperca chuatsi), a basic diet (control group) and five experimental diets with additional 40 mg/kg of Zn designed in this experiment. Five Zn sources are ZnSO₄, Zn-RAA (rice protein amino acid chelate zinc), Zn-SAA (soy protein amino acid chelate zinc), Zn-Met (1:1), and Zn-Met (2:1), respectively. A total of 270 S. chuatsi (initial weight 67.46 ± 2.02 g) were divided into six groups, each with three replicates of 15 fish, for a 49-day growth trial. Results showed that all zinc sources increased growth and feed conversion. Zn-Met (2:1) had the best effect, followed by Zn-Met (1:1), Zn-RAA, Zn-SAA, and ZnSO₄ had the least effect. The Zn-Met (2:1) group significantly enhanced muscle texture, optimized myofiber structure, and increased Zn deposition and collagen content in muscle. It also elevated intestinal Cu/Zn-SOD, T-SOD, and T-AOC activities, reduced MDA levels, and upregulated the mRNA expression of antioxidant genes like cu/zn-sod, nrf2, gpx1, and cat. This group improved intestinal digestive and absorptive enzymes activities, reduced intestinal damage and inflammation, decreased Endotoxin and D-LA levels, and increased IgM content. Proinflammatory cytokines (il-8, il-1β, tnf-α) were downregulated, while the anti-inflammatory gene tgf-β1a was upregulated. 16S rRNA sequencing showed an increase in the relative abundance of beneficial bacteria and α-diversity. Overall, amino acid-chelated zinc outperforms zinc sulfate in promoting growth, improving muscle quality, antioxidant and immune functions, and enhancing intestinal health, with Zn-Met (2:1) having the best effects.