Murray cod (Maccullochella peelii (Mitchell, 1838)) is an iconic Australian species, initially farmed mostly for stocking but now also for human consumption. Here, we report an infection with Dermocystidium sp., class Mesomycetozoea, order Dermocystida in the gills of Murray cod, from a hatchery in south-eastern Australia. Based on phylogenetic analyses of the 18S ribosomal DNA the parasite was closely related to D. salmonis, however the size of the spores was smaller than that reported for D. salmonis in other parts of the world. Further studies using additional analyses including ultrastructure of the spores would be useful for elucidating the identification of the microorganism. Histopathology showed inflammatory response and epithelial hyperplasia resulting in lamellar fusion particularly in association with the parasite. The condition was diagnosed as branchitis caused by a co-infection with Dermocystidium and epitheliocystis, with Dermocystidium being the dominant pathogen.