Coccidiosis due to Goussia lomi (Protista: Apicomplexa) in aquarium-reared Murray cod, Maccullochella peeli

Intestinal parasitism by the coccidian Goussia lomi was associated with morbidity and histological lesions in aquarium-reared Murray cod fry, Maccullochella peeli (Mitchell), at a hatchery near Narrandera, New South Wales, Australia. Coccidial infection was not found in pond-reared Murray cod of the same age, nor in trout cod, M. macquariensis (Cuvier & Valenciennes), reared under similar conditions at the same hatchery. Overcrowding may have predisposed Murray cod in aquaria to heavy infection with G. lomi. Clinical coccidiosis was expressed in a small proportion of infected fish. Large numbers of coccidial developmental forms were detected histologically in the intestinal mucosa of affected fish in association with a necrotic enteropathy. Using a method of intestinal trypsin digestion and flotation, 2000 coccidial oocysts were counted in one 0.05 g fish.