Studies or the effect of phosalone (an organophosphate) on changes in haematological indices were made in a snake headed murrel fish, Channa gachua (Ham.). The mean values of Hb content, RBC count, Haemalocrit values, M.C.H.C. and Oxygen capacity in control group of fishes were 15.2+0.18 (g%), 2.86+0.11 (million cells/mm of blood), 23.8+1.18, 63.8 (%) and 19.0 (Vol%) respectively. Treatment of acute sub lethal dosage (8.0 ppm) of phosalone brought statistically significant decrease in most of the blood parameters except M.C.H.C. in experimental animals. The reason for such changes has been discussed in this paper.