Effect of Season on Genotoxicity and Heavy Metal Accumulation in Oreochromis niloticus and Clarias gariepinus from the Lower River Niger, Nigeria

Abstract

Abstract

The level of heavy metal concentration and genotoxicity was assessed in both Oreochromis niloticus and Clarias gariepinusfrom the Niger River, Nigeria. Fish samples were collected both during the dry and wet season between April, 2017 and September, 2018. Aluminium (Al), Chromium (Cr), Copper (Cu), Iron (Fe), Nickel (Ni), Zinc (Zn), Mercury (Hg), Arsenic (As), and Lead (Pb) concentrations in fish samples were also analysed using Inductively Coupled Plasma Optical Emission Spectrometroscopy (ICP-OES). Result showed higher accumulation of heavy metals in both fish tissues in the wet season than the dry season. The highest accumulated heavy metal in the fish sample was Fe during the dry seasons [(Fe (O. niloticus) = 64.28±12.93 mg/g, Fe (C. gariepinus)]= 96.06±58.36 mg/g) and wet season [Fe(O. niloticus) = 67.42±14.11 mg/g, Fe (C. gariepinus)] = 99.16±59.36 mg/g). Heavy metal accumulation evaluated followed the trend Fe > Al > Cd > Zn > Pb > Cu > As > Ni > Cr > Hg for the dry season and Fe > Al > Zn > Cu > Pb > Cr > Ni > Cd > As > Hg for the wet season in O. niloticus; and Fe > Al > Zn > Pb > Cu > Cr > Ni > Cd > As > Hg for the dry season and Fe > Al > Zn > Pb > Cu > Ni > Cr > Cd > Hg > As for the wet season in C. gariepinus. Most of these heavy metals were beyond international permissible limits. The four polymorphic RAPD markers used in the study showed more polymorphisms in C. gariepinusthan O. niloticusin both the dry and wet season. There was no difference in the polymorphic bands between dry and wet season in O. niloticus while more polymorphic bands were observed in wet season (50 bands) than dry season (47 bands) tissues of C. gariepinus. The result indicated a lower Genomic template stability (GST) in C. gariepinus (dry = 2.70, wet = 5.41) than O. niloticus (dry = 13.16, wet = 13.16) when compared in both seasons. This study revealed the level of toxic metal accumulation and genotoxic potentials of these fishes in the food chain of locals consuming them. Drastic measures are of high necessity in order to protect both the aquatics and potential consumers in the area.