Effects of short-term sub-lethal diazinon® exposure on behavioural patterns and respiratory function in Clarias batrachus: inferences for adaptive capacity in the wild

Abstract

ABSTRACT The potentials for neurotoxicity and respiratory distress under 96 h acute diazinon exposures was examined using behavioural indices and opercular movement respectively in walking catfish, Clarias batrachus. Diazinon exposure concentrations were correlated with toxicological (lethal and sublethal) endpoints. The LC50 values and 95% confidence limits at 24, 48, 72 and 96 h, were 21.85 (19.09- 28.199 mg/L), 19.081 (17.15-21.65 mg/L), 16.07 (14.49- 17.86 mg/L) and 12.85 (10.92-14.39 mg/L) respectively. Concentration-dependent mortality and altered behavioural responses including uncoordinated swim movements, excessive mucus secretion, imbalanced and erratic swimming patterns and brief inactivity prior to mortality was observed. The altered behavioural patterns reflecting neurotoxicity, and increased opercular movement indicating respiratory distress in the catfish increased proportionally with elevated levels diazinon and exposure time. The inactive and almost non-motile state prior to death indicates paralysis and muscle seizure typical in the late stages of cholinergic toxicity. The severity of behavioural and respiratory effects on adult C. batrachus, a hardy species, portends catastrophic consequences for less hardy and more susceptible aquatic taxa like fish in the field, including considerable loss of adaptive ability.