Effects of Abattoir Effluent on Growth Performance of Clarias gariepinus (Burchell, 1822)

This study investigated the acute and sub-chronic toxicological effects of untreated abattoir effluent on juvenile Clarias gariepinus (African catfish), with the aim of assessing its impact on fish behavior, survival, growth performance, and bioaccumulation of heavy metals. Effluent samples were collected from the discharge point of Alubarika abattoir, located in Ile-Ife, Osun State, Nigeria. Standard analytical methods were used to determine parameters such as pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), electrical conductivity, total dissolved solids (TDS), and concentrations of heavy metals (Cd, Pb, Fe, Cu and Zn). Acute toxicity testing was carried out by exposing juvenile C. gariepinus to six concentrations (0%, 12.5%, 25%, 50%, 75%, and 100%) of the effluent over 96 hours to determine LC₅₀. Sub-chronic tests were conducted over 30 days using lower concentrations (0%, 2.5%, 5%, 7.5%, and 10%) to assess growth, behavior, feed utilization, and metal accumulation in fish tissues (gill, muscle, liver, and gastrointestinal tract). The results revealed that the effluent had BOD (6350 mg/L), electrical conductivity (3321 µS/cm), TDS (2220 mg/L), and heavy metal concentrations exceeding both NESREA and WHO standards. Behavioural stress responses such as erratic swimming, surfacing, and discolouration were observed in fish exposed to concentrations 50% and above. Mortality rates increased with concentration, with 100% mortality recorded in 50%, 75%, and 100% treatments within 48 hours and 96-hour LC₅₀ of 35.4 mg/L. In the sub-chronic phase, fish exhibited varying growth responses. Weekly measurements showed that while all groups experienced some level of growth, the highest mean weight gain (116.27 ± 2.50 g) was observed in the 7.5% treatment, whereas the lowest performance occurred in the 2.5% group. Specific growth rate (SGR), daily feed intake (DFI), and percentage weight gain (PWG) varied inconsistently across treatments. Heavy metal accumulation showed a dose-dependent increase, with the highest concentrations of Cd, Pb, Fe, Cu, and Zn found in fish exposed to the 10% effluent, particularly in the gills and gastrointestinal tract. The study concluded that untreated abattoir effluent significantly degrades water quality, induces acute toxicity, alters growth dynamics, and promotes bioaccumulation of toxic metals in C. gariepinus. There is an urgent need for abattoir waste treatment and effective regulatory enforcement to mitigate environmental pollution and ensure the safety of aquatic food sources.