Biological Science: Research Developments and Innovations Vol. 6

Rogor (dimethoate), an organophosphate pesticide, can enter freshwater systems and affect non-target fish at sub-lethal concentrations. This laboratory study examined dose- and time-dependent behavioural responses of the freshwater air-breathing fish Channa punctatus following exposure to fractions of a predetermined 96-h LC₅₀ of 0.74 mL/20 L. Fish were assigned to a control group and three treatment groups receiving 1/5 LC₅₀ (0.148 mL/20 L), 1/3 LC₅₀ (0.247 mL/20 L), or 1/2 LC₅₀ (0.370 mL/20 L). Opercular movement, surfacing frequency, locomotor activity, feeding response, and stress-related abnormalities were assessed at 48, 72, and 96 h and at 10, 20, 30, and 40 days. Behavioural disturbances generally increased with concentration and exposure duration. Group B showed comparatively transient changes, whereas Groups C and D displayed more persistent increases in opercular movement and surfacing, reduced swimming performance, delayed feeding, lower food consumption, and higher stress-severity scores. By day 40, Group D showed a 62% reduction in mean swimming velocity and marked feeding suppression. Mortality was recorded in Groups C and D but not in the control or Group B. Principal component analysis indicated clear dose-related separation of behavioural responses, with sustained multi-endpoint impairment evident at higher exposures. Within the controlled laboratory conditions, these findings show that prolonged Rogor exposure was associated with progressive behavioural disruption in C. punctatus and support the use of behavioural endpoints alongside conventional toxicity measures.