The present study aimed to investigate effects of the heavy metal Cd on the sperm morphological indices of Caspimyzon wagneri. The sperm were exposed to 0.01, 0.1, 1, 10, 100 and 1000 mg.L-1 Cd for three minutes, three and 36 hours. The sperms exposed to Cd showed an increase in the length, width and surface of the head, flagella degradation and slightly flagella breakage. With increase of Cd concentration or the exposure duration, the damages found in sperms increased. But when exposure to

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... aminant exceeds than certain period of time, damage effects caused changes in the sperm structure as head length reduction and head width increasing and thereby reducing the sperm's head surface, complete cutting of flagella at all samples and deformation of the sperm's head from oval to circular, which these changes became visible during 36 hours of exposure to cadmium. Therefore, the results revealed that the arrival of pollutants including cadmium to the natural reproduction ground of this species due to induction the harmful effects on sperm morphology factors will have adverse effects on sperm function and fertilization rate and reduce them, and as such will be considered a serious threat to the survival generation of this rare species.