The study evaluated the toxicity of aqueous extracts of Ricinus communis leaf on the juveniles of Heteroclarias, with mean weight 24.00 ± 0.25 g. Fish were exposed to varying concentrations of C (0.0, 2.0, 3.0, 4.0., 5.0 and 6.0 g/l), in a static bio-assay procedure for 96 hours. The 96 hours LC50 values were calculated at 4.37 g/l. Results indicated varying concentrations of R. communis resulted in different pathological alterations in the juveniles of Heteroclarias. Behavioural responses observed in experimental fish includes; erratic swimming, twitching, gaping, mucous discharge, skin discoloration and death. These responses and mortalities were significantly different (P˂0.05) in treatments with increasing concentration of R. communis when compared with the control. Experimental water showed increase in temperature (°C), pH and conductivity (µS/cm) with increase in test ingredient concentration while reverse was the case with dissolved oxygen (mg/l). Histolopathological assay of gills, liver and kidney, revealed different alterations in architecture, fragmentation and haemorrhage of gill filaments, fusion of the primary and secondary lamellae. Liver showed congestion of hepatic veins and foci hepatocellular degeneration while kidney revealed congestion of the renal artery, inflammation of the renal tubules, haematopoietic cells and nephrons, hyperplasia of the glomerular vessels, pyknotic nephrons and degenerated renal corpuscle.