Analysis of Dissolved Trace Metals in Aquaculture Pond Water and Fish Tissues in Kwara State

Fish farming ponds in Nigeria are often situated in areas exposed to agricultural runoff, atmospheric deposition, and effluent from upstream activities, potentially leading to the accumulation of trace metals in both pond water and cultured fish. This study analyses dissolved trace metal concentrations in aquaculture pond water and selected tissues of Clarias gariepinus and Oreochromis niloticus cultured in ponds in Kwara State, North Central Nigeria. Water and fish tissue samples were collected from six fish farms across two local government areas. Water was analysed directly by inductively coupled plasma optical emission spectrometry after filtration. Fish muscle, liver, and gill tissues were digested using a nitric acid-hydrogen peroxide mixture. Metals analysed include copper, zinc, lead, cadmium, manganese, and iron. Bioconcentration factors were calculated for each metal-tissue combination. Results show that zinc and iron were the most abundant trace metals in both water and fish tissues. Lead and cadmium, though present in low concentrations in pond water, showed preferential accumulation in liver tissue, with bioconcentration factors exceeding one. Gill tissue displayed the highest concentrations of most metals, consistent with direct water contact. Metal concentrations in muscle tissue were within FAO-WHO limits for human consumption in most samples. The study recommends baseline metal monitoring of aquaculture ponds and regular fish tissue analysis as part of aquaculture management practice. Keywords: trace metals, aquaculture, Clarias gariepinus, Kwara State, bioconcentration