Effect of papaya leaf extract on growth performance, skin mucosal immune responses, liver enzymes, disease resistance, and tight junctions of Cyprinuscarpio.

Abstract

This study evaluated the effects of Carica papaya L. leaf extract (PLE) as a feed supplement on growth performance, skin mucosal and haematological immunity, and gene expression in carp Cyprinus carpio. Diets containing PLE (g kg): 0&#xa0;g [control], 0.5 (P1), 1.0 (P2), 1.5 (P3), 2.0 (P4), and 3.0 (P5) were fed to the fish for 60 days. PLE at 2.0&#xa0;g/kg maximized the growth performance of fish. Among haematological parameters examined, RBC, Hb, and serum protein levels were significantly higher in P4. Intestinal lipase and protease activities were high in P3 and P4. Skin mucosal lysozyme, alternative complement pathway, alkaline phosphatase, peroxidase, and protein levels were significantly higher in P3 and/or P4 than in the control. Furthermore, liver SOD and CAT levels were significantly enhanced in P3 and P4; whereas, dietary PLE did not influence liver MDA and GPx levels. The expression of il-1&#x3b2; was down-regulated (P&#xa0;<&#xa0;0.05) in P4. Conversely, il-10 expression was strongly upregulated in the intestine at P3&#x2012;P5. Expression of occludin and claudin7 was significantly higher in P2&#x2012;P4; however, the mRNA abundance of zo-1 was higher (P&#xa0;<&#xa0;0.05) at P4 cells only. The expression of sod, cat, and nrf2 was significantly upregulated in the liver at P3 and/or P4; whereas, expression of keap1 was strongly down-regulated in P4. Fish from P4 exhibited higher relative post-challenge survival (68.89&#xa0;%) against Aeromonas hydrophila challenge. Dietary supplements of PLE at 2.0&#xa0;g&#xa0;kgcan significantly improve the growth, intestinal enzymatic activities, skin mucosal immune parameters, and liver antioxidant responses, and strengthen the immunity of C. carpio.