A total of 780 Fingerlings fish (390 Tilapia nilotica and 390 Cyprinus carpiol (common carp) were utilized for studying the toxicological effect of mercury, cadmium and lead as water pollutant heavy metals. The LC₅₀ clinical signs, P. M. lesions, pathological changes and residual concentration were determined.
The results showed that the LC₅₀ of mercuric chloride and cadmium chloride were 5.525 mg/L and 8.075 mg/L, respectively for Tilapia nilotica and 4.425 mg/L and 5.925 mg/L, respectively for Common carp. There are no mortalities among both fish species subjected to lead acetate within 96 hrs. The intoxicated fish by the three heavy metals showed the same Signs of nervous and respiratory manifestation as well as hepatic and renal disorders. The residual concentration of mercuric chloride; cadmium chloride, and lead acetate were 1. 64 ± 0.04, 1.47 ± 0.02 and 3.70 ± 0.08, respectively in tissues of Tilapia nilotica and 2.85± 0.29, 2.18 ± 0.12 and 4.95 ± 0.17, respectively in tissues of Common carp.