Freshwater fish, Labeo rohita, were exposed to sublethal concentration (0.5 μg·L-1) of cypermethrin for 7 and 15 days to examine the bioenergetics in functionally four differnt tissues, namely, gill, liver, brain and muscle. Whole animal oxygen consumption was measured first and it was found to decrease in both the exposure periods (EPs), manifesting respiratory distress of the animal in toxic environment. Ionic regulation and energy requirements were also found to be altered under stress, as observed by the inhibition of both Na+/K+ and Mg2+ ATPases at 7d EP and elevation at 15d EP. Increase in glucose-6-phosphate dehydrogenase (G-6-PDH) was consistent with the increase in exposure time.Attenuation of acid and alkaline phosphatases were noticed in treated fish after 7 days but were close to normalcy at 15d EP. These results clearly indicate that the fish were affected at 7d EP but adapted to the toxic environment within 15 days. It shows that at this concentration cypermethrin is only moderately toxic and the animal has alternate pathways to derive energy and survive. Freshwater fish, Labeo rohita, were exposed to sublethal concentration (0.5 μg · L-1) of cypermethrin for 7 and 15 days to examine the bioenergetics in functionally four differnt tissues, namely, gill, liver, brain and muscle. was measured first and it was found to decrease in both the exposure periods (EPs), manifesting respiratory distress of the animal in toxic environment. Ionic regulation and energy requirements were also found to be under stress, as observed by the inhibition of both Na + / K + and Mg2 + ATPases at 7d EP and elevation at 15d EP. Increase in glucose-6-phosphate dehydrogenase (G-6-PDH) was consistent with the increase in exposure time. Attenuation of acid and alkaline phosphatases were noticed in treated fish after 7 days but were close to normalcy at 15d EP. These results clearly indicate that the fish were affected at 7d EP but adapted to the toxic environment within 15 days. It shows that at this concentration cypermethrin is on ly moderately toxic and the animal has alternate pathways to derive energy and survive.