Healthy fishes of Oreochromis niloticus and Clarins gariepinus were exposed to different lethal and sublethal concentrations of carbaryl (sevin) as carbamate hydrocarbon which is an acetylcholine estrase inhibitor used as insecticide. The 96 hours LC50 for both fish species was computed as 4.45 mg/l_i for Oreochromls niloticus and 17.55 mg/T3 for danns gariepinus. The fishes showed remarkable changes in behaviour after exposure, The behaviours observed were; cough, yawn, Fm flickering, jerks, threat, and nip etc. They showed hyperexcitation-lethargy and occasional darting movements and sometime losing balance (in catfish) due to hanging upside down and rolling on the surface of water in the tank. After 96 hours of fish exposure to sub-lethal concentrations of the insecticide, significant depletion of muscle, liver and brain tissue glycogen (P<0.001) was recorded. On the other hand, the level of depletion of glycogen content was more prominent in