Effects of Mentha longifolia extract on some blood and immune parameters, and disease resistance against yersiniosis in rainbow trout

Abstract

The aim of this study was to investigate the effects of horsemint (Mentha longifolia) hydroalcoholic extract on blood parameters, serum, mucosal immune responses, and expression of immunity-related genes in rainbow trout (n = 360; 10.48 ± 0.2 g). The fish were fed with 0.0, 0.1, 0.2, and 0.3% of horsemint extract in 12 aquaria (100 L) with three replicates (each with 30 fish) for 4 weeks. Blood and serum immune indices, mucosal protein pattern, and expression of alpha-tumor necrosis factor (TNF-α) and lysozyme genes were evaluated at the end of feeding trial following challenge with Yersinia ruckeri. The results of measured experimental indices revealed significant differences in both RBC and WBC counts, hematocrit, hemoglobin, complement, lysozyme, neutrophil, respiratory burst, total protein, and albumin among the fish fed with 0.3 and 0.2% of the extract and control group. The number and density of bands were different in the mucosal protein patterns between the fish received M. longifolia extract. Also, the expression of lysozyme and TNF-α genes increased significantly in the extract-fed fish compared to the control. The protective effect of horsemint extract in the challenge of fish with Y. ruckeri in different treatments showed that a 0.2% inclusion level led to significant rises in both blood and serum immune indices. The fish fed with 0.3% of complementary extract presented elevated number and density of mucosal protein pattern bands in comparison to control group. Post-challenge TNF-α gene expression was higher in fish received high levels of horsemint extract than in the control group. Based on the findings, the improvement of hematological and mucosal immunity indices as well as increased expression of lysozyme and TNF-α genes in fish treated with 0.2% of M. longifolia extract could have resulted from the positive effect of this compound on immunogenisity and increased resistance to bacterial disease in rainbow trout.