Abstract

Two goldfish (Carassius auratus) from the same aquarium system were presented approximately one year apart for similar signs of severe abdominal distention, chronic intermittent buoyancy problems, and multiple superficial skin lesions. At necropsy, multifocal small white nodules were observed in the tissues of the liver and kidney, and a larger mass was suspended in the abdominal mesentery. Histopathology revealed numerous discrete granulomas each having an encapsulated central amorphous eosinophilic area with karyorrhectic debris. Within the liver and mesenteric mass, areas of chronic inflammation were observed with several large distinct pyogranulomas, each comprised of a zone of macrophages and multinucleated cells surrounding a central core. Each central core consisted of either necrotic and degenerating neutrophils or amorphous eosinophilic granular material. The pyogranulomas were often encapsulated by a few layers of immature fibrous connective tissue. Areas of inflammation featured clusters of low to moderate numbers of spherical protozoan organisms approximately 2-3 micron in diameter. Intact organisms were most commonly noted in a narrow zone adjacent to the necrotic cores of some pyogranulomas. Additional stains were used to evaluate the tissues. The PAS reaction was variably positive for granular material within the protozoan cytoplasm, while Brown and Hopps and Ziehl-Neelsen stains did not reveal additional organisms. Severe chronic multifocal pyogranulomatous hepatitis and peritonitis with intralesional protozoa was diagnosed. Previous reports of this parasitic infection have classified the organism as an amoeba, most likely in the family Hartmannellidae. Veterinary pathologists and fish health professionals should be aware of this organism as another cause of granulomatous disease in goldfish.