Cytogenotoxicity Effects of Some Selected Heavy Metals on Oreochromis niloticus and Clarias gariepinus


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Toxicity, Heavy Metals,`, Micronuclei,, Nuclear Aberration, Fish



The contamination of natural waters by heavy metals depreciates aquatic biota and poses considerable environmental risks and concerns. This study investigated the cytogenetic abnormalities associated to Oreochromis niloticus and Clarias gariepinus exposed to some selected heavy metals [Mercury (Hg), Zinc (Zn), Lead (Pb) and Nickel (Ni)] using micronucleus (MN) and nuclear abnormalities (NA) tests in peripheral erythrocytes. Acute toxicity bioassay was conducted in a semi static system to determine the 96-h LC50 value of the test chemicals following standard methods. The sublethal doses for all the heavy metals used were calculated as 75% of the obtained LC [Sub Lethal dose 3 (SL3)]. Fishes were exposed to SL3 for 21 days 50 after which they were harvested and the cytogenetic toxicity endpoint assessed. The NAshapes were scored into binucleated cells, micronucleated, notched, blebbed, vacuolated, dumb-bell shaped and deshaped nuclei. Result of acute toxicity showed that lethality increased with increase in heavy metal concentration. It was observed that, fish species showed significant sensitivity to the different heavymetalstreatment.In general,the highest value of bothMNandNA cells were significantly increased in the exposure and followed trend as Hg > Pb ?Zn ?Ni. On the other hand, C. gariepinus was more sensitive to the three heavy metals exposure than O. niloticus. The frequencies of each NAshape were found in all the fish species and in all the treatments as follows NT>LB>BN>BL. Results showed that the exposed fishes showed cytogenetic alterations in their genetic materials. Heavy metals in natural water body can be bio accumulated and biomagnified in fish and consumption of such fish contaminated with metals thus poses a risk to human health.