Concentrations of heavy metals Aluminium (Al), Chromium (Cr), Copper (Cu), Iron (Fe), Nickel (Ni), Vanadium (V) and Zinc (Zn) were analyzed in the tissues of two estuarine fish species; Tilapia (Sarotherodon melanotheron) and silver catfish (Chrysichthys nigrodigitatus) from Okrika estuary in the Niger Delta area of Nigeria. The sampling was conveyed in two seasons, October/November, 2015 and January/February, 2016, representing the climax of both wet and dry seasons respectively. The levels of the metals in the fish species were analyzed by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). The sequence of the metal accumulations in Tilapia was; Fe > Al > Zn > Cu > Cr > V > Ni, in silver catfish; Fe > Al > Zn > Cu > Cr >Ni > V. Levels of the metals in the fish species were higher than the international permissible limits based on the criteria or application of relevant pollution indices. This indicates that the two fish species were not fit for human consumption. A two way analysis of variance (ANOVA) was used to test the difference in metal concentrations in the fish tissues. Mean differences were separated by the use of t-test. In comparison of the metal accumulations in the tissues of the fish species from oil impacted creeks (Ekerekana, Okari and Ogoloma) and non or less oil impacted counterpart (control site), higher levels (p<0.05) of the metals were observed in the impacted than the non-impacted creek. For most of the metals, Sarotherodon melanotheron had higher concentrations than the Chrysichthys nigrodigitatus. Seasonal variations reflected that there was higher accumulation of the metals in the two fish species in the rainy season than the dry season. Pearson Correlation Analysis and the use Vanadium/Nickel ratio were used to confirm the source of the metals in the fish from oil pollution. Therefore, it is mandatory and expedient to ensure regular monitoring of the trace element loadings in these creeks and to take appropriate measures to alleviate the incidence in order to safeguard the health of the public.

Keywords: heavy metals; tilapia; silver catfish; Okrika estuary; Niger-Delta