Abstract

The toxicity and behavioural response of fingerlings of Clarias  gariepinus  (mean total length, 5.04± 0.7cm; mean body weight 4.05 ± 0.3g) to inorganic fertilizers ( NPK, 20:10:10) was studied under laboratory conditions to determine the acute toxicity of NPK, 20:10:10 fertilizer to fingerlings of Clarias gariepinus using a static bioassay test. The fingerlings were exposed to increasing concentrations of NPK, 20:10:10 (0.00g/l, 8.00g/l, 12.00g/l, 16.00g/l and 20.00g/l,) fertilizer in the static renewal bioassay for 96 hours. Exposed fish showed behavioural responses such as agitated swimming, air gulping, restlessness, loss of balance, caudal, frequent attempts at jumping out of the tank and quietness. Water quality examinations showed a decrease in the dissolved oxygen content and increase in total hardness and alkalinity as the concentration of fertilizer was increased. Clarias gariepinus fingerlings were more susceptible to fertilizer NPK, 20:10:10 at higher concentrations as indicated by the percentage of death in the results and the LC₅₀= 12g/L, safety limit =1.20g/L. The concentrations of the toxicants were dose dependent and caused changes in skin colouration of the fish, mortality was highest in the highest concentration of fertilizer and no mortality in the control. Mortality rates were concentration-dependent and death rate in the highest concentrations were significantly higher (P<0.05) than the others. Mortality rate was influenced by both concentration and time. The findings from this study show that NPK, 20:10:10 fertilizer could be classified as toxic to Clarias gariepinus fingerlings at certain concentrations. 

Key Words: Strain, Fertilizer, Fingerlings, Toxicosis and Clarias gariepinus