Abstract:
The effects of prolonged exposure of copper through sub-lethal toxicity test using Nile tilapia (Oreochromis niloticus) fingerlings was investigated using five nominal copper concentrations (control, 0.1819, 0.3638, 0.7276 and 1.0914 mg L-1 ). Throughout 21 days of exposure, tilapia fingerlings were harvested at 7, 14 and 21 days for mean copper accumulation detection through ICP-MS, investigation of cell damage through Single Cell Gel Electrophoresis and determining DNA structure alteration through RAPD-PCR analysis. The 96-h LC50 value for Nile tilapia fingerlings was calculated to be 1.819 mg
L- 1 • Accumulation of copper was studied on four different parts; muscle-tissue, viscera, gills and whole fingerling body. The uptake of copper varied in an order from highest concentrations; viscera> whole body > gills > muscle-tissue. Highest Cu2+ concentration accumulated by viscera was 690.4904 μg g- 1 at 21 days. At cell level, damage induced by Cu2+ in tilapia fingerlings showed a significant increase in DNA tail percentage in 7 and 14 days of exposure, indicating DNA damage was observed at all concentrations compared with control (P<0.05). A gradual decrease in the mean DNA tail percentage was observed at 21 days indicating repair of the damage DNA. The mean DNA tail percentage showed a dose-related increase and time dependent decrease after the treatment with Cu2+ when compared to control. RAPD pattern displayed some changes in
polymorphism band patterns in exposed Nile tilapia fingerlings. The disappearance of bands was found in highest Cu2+ concentration (1.0914 mg L- 1 ) for primer OPB 7 at band molecular size of 500 bp in 14 and 21 days of exposure. Disappearance of bands proved that DNA fragment of exposed tilapia were altered signifying that DNA damage had Xll occurred. Therefore, results in the present study proved that Cu2+ is significantly known as genotoxic compound to Nile tilapia fingerlings as damage in cell level and DNA fragment alteration was detected.
