Dietary Polygonum minus extract ameliorated the growth performance, humoral immune parameters, immune-related gene expression and resistance against Yersinia ruckeri in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effects of Polygonum minus extracts on growth performance, skin mucus and serum immune parameters as well as immune-related gene expressions in rainbow trout. For this purpose, rainbow trout (mean weight: 50 ± 2.2 g) were fed experimental diets containing different levels 0 (control), 5, 10 and 15 mg/kg diet of P. minus for 8 weeks. At the end of the trial, the results showed that final body weight, weight gain and specific growth rate were significantly increased in fish fed diets containing P. minus (P < 0.05). In addition, the feed conversion ratio of fish treated with P. minus was significantly decreased (P < 0.05) compared to the control group. The blood RBCs, WBCs, Hb, total protein, albumin, and globulin showed a significant increase with decreased alkaline phosphatase (ALP) and alanine aminotransferase (ALT) in fish treated with P. minus compared to the control treatment. The blood lysozyme activity and total Ig showed significantly higher values in fish fed P. minus at 10 or 15 mg/kg than the other groups, while the respiratory burst activity increased significantly in fish fed P. minus at 15 mg/kg diet than the other groups (P < 0.05). The skin mucus total protein and esterase increased significantly in fish fed P. minus at 15 mg/kg diet than the other groups (P < 0.05), while the skin mucus alkaline phosphatase, protease and lysozyme activity increased significantly in fish fed P. minus at 10 or 15 mg/kg diet than the other groups (P < 0.05). The relative immune gene expressions (IL-1β, IL-8, and lysozyme) upregulated relatively in fish fed P. minus at 15 mg/kg diet than the other groups. The relative expression of TNF-α upregulated in fish fed P. minus at 10 or 15 mg/kg diet. The cumulative mortality of rainbow trout subjected to Yersinia ruckeri infectious exhibited relatively low mortality levels in all supplemented groups with the lowest being in fish fed 15 mg/kg P. minus. Highest percentage survival (%) rate was found in the 15 mg P. minus per kg diet. The results of this study confirm the beneficial effects of dietary P. minus on growth performance and immune parameters of rainbow trout.