Richard E. Wolke, DVM, PhD
Sea Grant Marine Pathology Laboratory, University of Rhode Island, Kingston, RI
Abstract
History, etiology and prevalence of piscine Mycobacteriosis (tuberculosis) are discussed and its economic importance to the aquarist and aqua culturist is considered.
Characterization of recent isolates from marine and fresh water fish and their passage from fish through mice to fish is reported and public health significance discussed.
Gross and histopathologic lesions are described with special emphasis on the differential diagnosis of piscine tubercles from other granulomata found in the fish.
Notes
Mycobacteriosis is common in commercial fisheries and aquariums but rare in feral populations. The diagnosis is made by doing an acid fast stain of the granulomas. In the acute phase of the disease there is a weakly encapsulated tubercle with a central area of caseous necrosis and epithelioid cells present. The organisms can be seen on acid-fast stain.
Piscine vs Mammalian T.B.
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Bacilli
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Giant Cells
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Cavitation
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Piscine
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+4
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-
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-
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Mammalian
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+1
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+
|
+
|
Differentials
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Flavo-bacteriosis
This is caused by a gram negative organism and occurs in freshwater tropical fish. Focal granulomata with caseous centers occur especially in the liver. It differs from mycobacteriosis in that the caseous center is surrounded by lymphocytes and macrophages rather than epithelioid cells and flavo-bacterium is not acid fast.
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Acanthocephalan
These occur in white perch and striped bass. Focal granulomas with caseous centers occur, however they have a four layer structure consisting of a fibroblast capsule, a layer of eosinophils, then another fibroblast capsule. There are no acid-fast bacteria present.
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Nocardia
This disease in fish is similar to that in the dog. Diffuse sheets of reticuloendothelial cells with small areas of necrosis occur. The disease differs from mycobacteriosis in that it is not so much a focal granuloma but is diffuse. Nocardia can be acid fast but it doesn't stain with the Ziehl-Nielsen stain.
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Corynebacterium
Kidney disease" is common in salmonids. Coryne-bacterium is gram positive and sometimes acid fast. Sheets of reticuloendothelial cells packed with gram positive organisms can be seen.