Immune Responses and Growth Performance of the Aqueous Methanolic Extract of Malva sylvestris in Oncorhynchus mykiss

Abstract

Growth promoting and immune stimulating effects of common mallow (Malva sylvestris) aqueous methanolic extract (AME) in O. mykiss were examined. Two different concentrations of common mallow AME [0.1 (CM1) and 0.5 (CM5) g kg-1 of feed] commixed a basic diet and a control diet without the common mallow extract were fed to rainbow trout for 30 days to evaluate growth rate and immune responses. At the end of the study, fish growth performance was determined as significantly higher in the group fed with 0.1 g kg-1 common mallow AME compared with control diet fed group (P<0.05). In fish fed with CM5 diet, oxidative radical production (ORP) was the highest (P<0.05). Similarly, myeloperoxidase (MPO) activity was increased significantly in CM5 group. Lysozyme (LYS) and phagocytic activities (PA) were not altered in treated fish groups compared to the control group (P<0.05). The pro-inflammatory (IL-1β, TNF-α1, IL-8,), anti-infammatory (IL-10), lymphocyte agonist (TGF-β) and cell-mediated immune regulatory, IL-12 cytokines were generally down-regulated insignificantly compared to control. Although, common mallow AME could not elicit cytokine-mediated immunity and resistance to bacterial pathogen, A. hydrophila in rainbow trout, elevation in ORP and MPO activities in treated groups and growth promoting effect were noticed at a low dose. Therefore, application AME of common mallow at 0.1 g kg-1 of feed as growth promoter and non-specific immunostimulant is advocated for rainbow trout.