Experiments were conducted to determine the toxicity of potassium cyanide (KCN) on juvenile Heteroclarias following a 96h static renewal bioassay method. Test specimens were acclimatized for 21-days prior to their exposure; the acute toxicity (LC50) was determined to be 0.96 mg/L. Fractions of LC50 (1⁄5, 1⁄4, 1⁄3 and ½) in triplicates were estimated for sub-lethal studies in a 21-day exposure/ recovery periods. Toxicity of KCN was assessed by examining the behavioural responses, growth parameters, survival rate, and histopathological alterations. Potassium cyanide induced behavioural responses such as irregular swimming activity, rapid jerk-like movement, loss of orientation, and subsequent mortality during lethal toxicity, and reduction in erratic feeding behaviour during sub-lethal exposure. Relative growth rate (RGR) and specific growth rate (SGR) were reduced during exposure, and there was no significant difference (P>0.05) in daily length increase (DLI). Condition factor (K ≥ 1) across the different treatments indicated the specimens were in good condition; and this could be due to cytochrome oxidase in catfish. Survival rate was 100%. Histopathological alterations in gills included lesions; severe stunting and multiple foci of erosion of the secondary lamellae. Fatty infiltration of the hepatic parenchyma and severe necrosis in liver were also observed. During the recovery period, improvements on the affected growth parameters (RGR and SGR), and tissues (gill and liver) were observed. Incidence of sub-lethal concentration of KCN in aquatic environment may induce physiological dysfunctions as indicated by reduced growth, gill and liver alterations in such organisms.

Keywords: Potassium cyanide; Heteroclarias; Histopathology; Growth; Survival.