Studies on the effect of Phosalone (an organophosphate pesticide) on histochemical changes in gills were made in a snake headed murre/ fish, Channa gachua (Ham. ). In the gills of control fish – Bromophenol blue test (for general protein), Alcian blue test (for acid mucosubstances) and PAS test (for carbohydrate substances) exhibited strong reaction both in the cartilagenous part of the gill arch and in the primary gill lame/lae. In phosalone treated fishes, their gills showed reduction in staining property (showing weak reaction) though there was difference in the staining intensities in acidophil cells, mucous cells, epithelial cells and central column of secondary gill lame/lae. The reason for such changes have been discussed in this paper.