The effects of dietary supplementation of mistletoe (Viscum album) extract on the growth performance, antioxidant, and innate, immune responses of rainbow trout (Oncorhynchus mykiss)

In the present study, rainbow trout fingerlings, Oncorhynchus mykiss, were fed diets supplemented with 0% (C), 0.5 (T1), 1.5 (T2), 2.5 (T3), and 4% (T4) mistletoe extract (ME), Viscum album over eight weeks. At the end of feeding trial, growth performance, serum antioxidant and innate immune responses, and serum bactericidal activity against Aeromonas hydrophila were evaluated. According to results, the highest final wight and wight gain (%), and the lowest feed conversion ratio (FCR) were observed in T2 and T3 treatments. Regression analysis showed that fish growth parameters were polynomially-related to dietary ME levels. The optimum dietary ME level, based upon the varied growth parameters, was 1.78 to 1.94%. The highest moisture content was observed in the control group followed by the T1 treatment, whereas the highest protein contents were observed in the T2 and T3 treatments. The lipid and ash contents were not affected by ME supplementation. Serum lysozyme, ACH50, total Ig, SOD, and bactericidal activity significantly increased in the ME-fed fish, with the highest values observed within the T3 treatment. The highest CAT and GPx values were recorded in the T2 and T3 treatments. ME treatment significantly decreased serum MDA levels, which was lowest in the T3 treatment. Serum ALT activities were similar in the T2, T3, and T4 treatments, and were significantly lower than those of T1 and control (C) treatments. Serum AST and ALP activities exhibited declines along with an increase in dietary ME levels; in which the lowest activities were occurred in the T4 treatment. In conclusion, dietary ME supplementation proved beneficial to rainbow trout, as it stimulated its growth performance, innate immune and antioxidant systems, and promoted bactericidal activity. Moreover, serum hepatic health indicators suggest that dietary ME may improve the fishes' hepatic health. © 2021 Elsevier B.V.