Dietary montmorillonite as growth promoter and immunomodulator in rainbow trout (Oncorhynchus mykiss).

A 98-day research was conducted to assess the influence of dietary montmorillonite (MMT) on growth and immune competence in rainbow trout (Oncorhynchus mykiss). Fish fry (mean weight: 500 ± 35 mg) were fed with four experimental diets contained MMT at levels of 0 (as control group), 1, 2 and 4%. At the end of the experiment, the survival rate and growth parameters and serum total protein and albumin levels in MMT experimental groups was higher than the control group. Regarding humoral immune responses, fish being fed with 2 and 4% MMT diets showed the greatest and the lowest serum C3, C4 and lysozyme levels, respectively. Serum alternative complement pathway activity (ACH50) in groups fed with 1 and 2% MMT supplemented diets was higher than the other groups. At the end of the challenge test with VHSV, the mortality rate reached to 28 and 20% in the control group and 4% MMT supplemented groups, respectively, whereas fish fed with 1 and 2% MMT supplemented diets showed the lowest mortality rate (2.5%) Fish fed with 1 and 2% MMT supplemented groups showed higher head kidney IL-1β and TNF-α genes expression compared to the other treatment groups. In addition, fish fed with 2% MMT-supplemented diet had the highest head kidney Lyz-2 gene expression. In summary, the results of this research suggests that supplementing diet with MMT at 1 or 2% improve growth and non-specific humoral immune responses and induce head kidney immune relate genes expression and disease resistance against VHS in O. mykiss.