Deaths in Australian freshwater fishes associated with Chilodonella hexasticha infection

The cause of the deaths of bony bream and other native fish in the Finke River near Alice Springs in winter 1984 was infection with the protozoan ciliate Chilodonella hexasticha. The parasites induced severe generalised epithelial hyperplasia in the gills, which would have compromised respiratory exchange and killed the fish through hypoxaemia. It is suggested that similar winter epizootics of ectoparasites have contributed to previous deaths of fish observed in the Finke River, in association with dry season conditions of low water temperatures and flow rates.