3-year-old Shubukin goldfish (Carassius auratus)Three-week history of progressive coelomic distention and exophthalmus. There was bristling of the scales and tachypnea.

Gross Description:  

A small amount of serosanguineous fluid was in the coelomic space and there were numerous adhesions between visceral surfaces. Numerous yellow-white foci, ranging from pinpoint to 2 mm diameter, were randomly distributed throughout the viscera and on both visceral and parietal coelomic surfaces. The swim bladder was distended with air. Cytologic examination of touch preparations of material from the coelomic space documented numerous macrophages and numerous 4 μm diameter, lightly basophilic round organisms (amoeba) with small eccentric to peripheral 1 μm diameter nuclei. Organisms were both free and within macrophages.

Histopathologic Description:

Tissue: Multiple caseous granulomas of variable size are within the liver, spleen and coelomic space. Concentric layers of fibroblasts form a thin capsule around many of the granulomas. A layer of macrophages surrounds the necrotic center and is mixed with lymphocytes, plasma cells and some heterophils. At the interface between the central necrotic debris and the surrounding mantle of macrophages are numerous, round, lightly eosinophilic organisms (amoeba), approximately 4 μm in diameter, with small eccentric nuclei.

Morphologic Diagnosis:  

Multifocal granulomas, liver, spleen, coelom, with intralesional amoebae


Hartmanella spp.

Contributor Comment:  

The histopathology of this case is similar to that previously reported.1 The amoeba was not cultured or classified but is believed to belong to the family Hartmanellidae. Amoebae have been found in many other fresh water aquarium fish species as well.

JPC Diagnosis:  

Coelomic viscera: Granulomas, caseating, multifocal to coalescing, with peripheral amoebae.

Conference Comment:  

Participants and the moderator were impressed by the extent of the granulomas and discussed the possibility of an additional infectious etiology, such as mycobacteriosis. Special stains failed to demonstrate bacteria (acid fast, Gram positive or Gram negative) or fungal agents. A differential diagnosis list for multiple coelomic granulomas in a goldfish would include granulomatous amoebic disease,(4) miscellaneous amoebic infection,(4) and mycobacteriosis.(3) Another focus of discussion was the presence of melanomacrophage centers (MMCs). Melanomacrophages are pigment-containing macrophages; most often they contain melanin, but they can have any pigment, such as ceroid or lipofuscin, within their cytoplasm. The pigment is often pink to golden in healthy fish and it becomes darker during periods of illness.(2) Melanomacrophage centers are discrete aggregates of melanomacrophages normally present in the kidney, spleen and liver.(2) They are also seen as part of the host response to foreign bodies and protozoal parasites. It has been found that the quantity, size and histomorphology of MMCs vary with age, season, nutrition status, and exposure to antigens.(2)


1. Dykova I, Lom J, Machackova B, Sawyer TK. Amoebic infections in goldfishes and granulomatous lesions. Folia Parasitologica. 43:81-90, 1996.

2. Ferguson HW. Systemic Pathology of Fish: A Text and Atlas of Comparative Tissue Responses in Diseases of Teleosts. Ames, IA: Iowa State University Press; 1989:7, 66, 92.

3. Hoole D, Bucke D, Burgess P, Wellby I. Diseases of Carp and Other Cyprinid Fishes. Ames, IA: Iowa State University Press; 1989:55-56,67.

4. Noga EJ. Fish Disease: Diagnosis and Treatment. Ames, IA: Wiley-Blackwell; 2010:264.

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