[Aim] The white spot disease, caused by the parasite Ichthyophthirius multifiliis is harmful to the Murray cod, Maccullochella peelii. The distribution and influence of I. multifiliis on the gills of M. peelii were investigated to better understand its pathogenicity and pathology and provide reference for the control of this disease in fish production.[Method] Light microscope and scanning electron microscope were used to identify the pathogen and describe its distribution on the gill-filaments, gill-lamella and the operculum of M. peelii.[Result] In infected M. peelii, I. multifiliis was distributed on the surface of gill-filaments, gill-lamella, operculum, under epithelial cells, between the gill-lamella or wrapped in mucus cells. The numbers of I. multifiliis on gill-filaments and gill-lamella were significantly fewer than on the operculum during the later period. In the late stage of infection, there was a certain degree of expansion and deformation of the gill-filaments, gill-lamella and operculum. Secretion by mucus cells increased, and the ends of the gills expanded and became deformed, even adhered and fused, and the top was globular or rod-shaped.[Conclusion] For the gills organs, I. multifiliis was mainly distributed on the operculum of M. peelii during the later period of infection. I. multifiliis caused the deformation of gill organs of M. peelii, which lost its normal function, blocking blood circulation and leading to unbalanced osmotic pressure, eventually causing death from hypoxia.