Abstract
Short-term static bioassays were made to evaluate effects of ambient temperature and daylight on the survival of freshwater catfish Heteropneustes fossilis to a lethal dose (1 μg/L) of cypermethrin. The results revealed that light hour exposure period (10 h) remaining constant, there was no mortality up to an ambient temperature of 3°C. Fish started dying as ambient temperature increased to 4°C and the mortality increased linearly with increase of temperature until 100% mortality was observed at an ambient temperature of 22°C. But mortality of the fish decreased with the increase of light hours at a constant ambient water temperature of 3°C.