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This study was carried out to evaluate the effect of concentration and duration of ichthyotoxic plants (Tephrosia vogelii, Adenia cissampeloides and Asystasia vogeliana) on the mortality rate of catfish (Clarias gariepinus). The total of 370 catfish were distributed into different aquaria containing the different concentrations (0, 25, 50, 75, 100 mg/l) of Tephrosia vogelii, Adenia cissampeloides and Asystasia vogeliana extracts, respectively with 10 animals in each aquarium using a completely randomized design (CRD) in a factorial layout. They were exposed to the extracts for 24, 48, 72 and 96 hours, respectively. The control group was also set under the same experimental conditions without the extracts. The result revealed that the extracts concentration had a significant effect (p<0.05) on the mortality rate of the fish. Also, the effect of the different durations was significant (p<0.05) on mortality rates of the exposed animals. Mortality rate was increased as the duration increased. The interaction effect between the concentrations and durations showed that the toxic effect of the extracts on the fish was more pronounced at the highest concentration and duration of exposure. Thus, this study has shown the potency of Tephrosia vogelii, Adenia cissampeloides and Asystasia vogeliana leaves extract as a fish poisoning plant suggesting that the use of the plants as a fishing stock should be regulated.