A total of 96 juvenile and 288 mature male and female Tilapia nilotica were exposed to mercury (Hg), cadmium (cd) and lead (Pb) pollution. The effects of such substances on some reproductive parameters were studied. The obtained results in mature treated fish revealed that the gonadosomatic index (GSI)decreased in the females after three weeks in cd and Pb exposed groups while in males a significant decrease in cd treated group and increase in lead treated group was recorded. The sperm count,

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... tility and its duration as well as fecundity showed significant decreases in all treated groups. Concerning Estradiol 17  and Testosterone, a significant decrease in each of gonads and skeletal muscles of treated males and females were observed. On the other hand, high mortality rate and retarded gonadal development in the juvenile fish were recorded.