Piscicidal effects of methanolic castor seed extract on catfish juveniles

Abstract

Traditional plants have been found useful for various purposes by the fish artisanals, but their toxicity on the fish is hardly considered. This study assessed the toxicity of castor (Ricinus communis) seed extract on catfish (Clarias gariepinus) juveniles in a static renewable bioassay. The study involved 500 fish samples collected from Motherhood Fish Farms, Nigeria. A stock solution of the methanol seed extracts, diluted in ratio 1:1 with water, was used for each treatment of the bioassay media concentrations in triplicates of 0 (control), 5, 6, 7 and 8 g L-1; following high mortality in 10 g L-1 determined in a finding range test. The LC50 and LC100 were calculated using probit method. The results showed that the irregular behavioural patterns and mortality rate of the test fish increased with increasing concentrations of the extracts at the intervals of 12 to 96 hr exposure. The serum results revealed that total protein values were significantly (p<0.05) different from the control. Levels of albumin increased in the fish blood serum, globulin fluctuated, while creatine, potassium and alkaline phosphatase decreased as the extracts’ concentrations increased over the control treatments. The gill structures showed deformation and liver showed cirrhosis across the concentrations but no recognisable changes on the control fish. There were adverse effects from extract concentrations 5 g L-1 and above. Therefore, indiscriminate use of castor seed on water bodies threatens the existence of catfish due to its piscicidal effects.