The effect of metrifonate on the immunity of the exposed fish are evaluated through the determination of the antibody titer and mortality rate during the challenge trial. In the chronic toxic exposure to metrifonate by dose 0.17mg/liter for 8 weeks, the more clear signs were darkness of fish color with hemorrhagic patches & loosing of scale at end of the trial the color return to normal. Determination of some blood parameters revealed significant decrease of white blood cell count, as there were lymphopenia and nueutrophilia during the chronic exposure to metrifonate. Phagocytic assay revealed a significant decrease in both phagocytic activity (PA) and phagocytic index(PI).Hypoproteinami hypoglobulinaemia and hypoalbuminaemia were observed. The challenge trial indicted that, the metrifonate decrease the immunity of exposed fish.. The using of biogen“R” as a growth promoter in fish diet minimized the toxicity of metrifonate.

Immunosuppressive, Metrifonate, Oreochromis niloticus

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