3-year-old Shubukin goldfish (Carassius auratus)Three-week history of progressive coelomic distention and exophthalmus. There was bristling of the scales and tachypnea.
A small amount of serosanguineous fluid was in the coelomic space and there were numerous
adhesions between visceral surfaces.Â 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.Â The swim bladder
was distended with air.Â Cytologic examination of touch preparations of material from the coelomic space
documented numerous macrophages and numerous 4 Î¼m diameter, lightly basophilic round organisms (amoeba)
with small eccentric to peripheral 1 Î¼m diameter nuclei.Â Organisms were both free and within macrophages.
Tissue: Multiple caseous granulomas of variable size are within the liver, spleen and
coelomic space.Â Concentric layers of fibroblasts form a thin capsule around many of the granulomas.Â A layer of
macrophages surrounds the necrotic center and is mixed with lymphocytes, plasma cells and some heterophils.Â At
the interface between the central necrotic debris and the surrounding mantle of macrophages are numerous, round,
lightly eosinophilic organisms (amoeba), approximately 4 Î¼m in diameter, with small eccentric nuclei.
Multifocal granulomas, liver, spleen, coelom, with intralesional amoebae
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.Â Amoebae have been found in many
other fresh water aquarium fish species as well.
Coelomic viscera: Granulomas, caseating, multifocal to coalescing, with peripheral amoebae.
Participants and the moderator were impressed by the extent of the granulomas and
discussed the possibility of an additional infectious etiology, such as mycobacteriosis.Â Special stains failed to
demonstrate bacteria (acid fast, Gram positive or Gram negative) or fungal agents.Â 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).Â Melanomacrophages are
pigment-containing macrophages; most often they contain melanin, but they can have any pigment, such as ceroid or
lipofuscin, within their cytoplasm.Â 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.Â It has been found that the quantity, size and histomorphology of MMCs vary with age, season, nutrition
status, and exposure to antigens.(2)
1.Â Dykova I, Lom J, Machackova B, Sawyer TK.Â Amoebic infections in goldfishes and granulomatous lesions.Â Folia
Parasitologica.Â 43:81-90, 1996.
2.Â Ferguson HW.Â Systemic Pathology of Fish: A Text and Atlas of Comparative Tissue Responses in Diseases of Teleosts.Â Ames, IA: Iowa State University Press; 1989:7, 66, 92.
3.Â Hoole D, Bucke D, Burgess P, Wellby I.Â Diseases of Carp and Other Cyprinid Fishes.Â Ames, IA: Iowa State University Press; 1989:55-56,67.
4.Â Noga EJ.Â Fish Disease: Diagnosis and Treatment.Â Ames, IA: Wiley-Blackwell; 2010:264.