The effect of sublethal concentration of certain pesticides with special reference to synergistic and antagonistic phenomenon on the calorific contents have been studied in an air breathing fresh water siluroid fish, Rita rita (Ham.). The calorific value of the control group of fishes was 3.82K.cal/g dry weight. The treatment of Metacid 50 (A), Dithane M-45 (B) and Kelthane EC (C) bring about significant decrease in calorific values. The combination of A+C, B+C, A+B, and A+B+C make the effect synergistic. The effective hirachy were in the following sequence -A+B>B+C>A+B+C>A+C. The TLm (24 h) values of different pesticides (including various combination) have also been calculated at 28.0±1.00C. The significance of this study as bioindicator and in water quality management has been discussed in this paper.