Saprolegnia diclina, which was the pathogen causing death in snake fishes(Channa argus) at culture farm, was investigated using scanning electron microscope. It was found that Saprolegnia diclina infection caused snake fishes to fail gas change in the gills. Cell lysis as well as edematous disease and hyperplasia as a result of Saprolegnea diclina attachment on the surface of gills were observed. The granules, the mean diameters of which ranged from 6 to $7;{mu}m$, attaching on the surface of gills were found to be secondary zoospores of Saprolegnia diclina. The failures of gas exchange in the gill cells and circulation as a result of the osmotic dilution of the blood were supposed to be the main cause of death.