Abstract

Many types of neoplasia have been documented in feral fish populations, and occasionally are seen in aquarium species and cultured fish.^1,2 Neoplasms can occur in virtually any tissue, with the most common locations in fish being skin, liver, and thyroid gland.^3-5 Accessions of captive freshwater and saltwater teleost fish submitted to the University of Illinois Zoological Pathology Program over a 13-year period were evaluated for neoplastic disease. Neoplasms were diagnosed in 64 of the 2,452 (2.6%) teleost biopsy and necropsy samples submitted from 1997 to 2010. The histopathology reports from the 64 captive teleost neoplasms were compiled to determine the distribution of tumor histogenesis (cell of origin), type of tumor diagnosed, and location of tumors.

There are a number of ways to classify neoplasms. Histogenic classification is based on histologic and cytologic examination of tissues to determine the cell type from which the neoplasm originated. Using this method, neoplasms can be divided into those that are derived from epithelial, neuroendocrine, mesenchymal, or round cell lineages, as well as "other", those that cannot be easily placed into one of the former categories. In this study, 24/64 (37.5%) of neoplasms were epithelial, 15/64 (23.4%) were neuroendocrine, 12/64 (18.8%) were mesenchymal, 9/64 (14.1) were round cell, and 4/64 (6.2%) were "other".

Although no species or family level trends were observed, some tumor types were diagnosed more often than others. For example, of the nine round cell neoplasms diagnosed, 100% were lymphoid in origin. Primitive neuroectodermal tumors (PNETs) represented 10 of the 15 neuroendocrine neoplasms. The morphologic and ultrastructural characteristics of PNETs in teleosts have been recently described.⁶ Fibrosarcoma/spindle cell sarcoma represented 5 of the 12 mesenchymal neoplasms, two of which were lepidocytomas, a neoplasia unique to fish. Of the 24 epithelial neoplasms, six were hepatocellular carcinomas, followed by four hepatocellular adenomas.

The tissue distribution generally correlated with previous reports, though no thyroid tumors were diagnosed in this investigation. In this review 14/64 neoplasms were hepatic, 14/64 were cutaneous, 11/64 were ocular, 11/64 were associated with the hemolymphatic system, and 5/64 were renal. Other less often represented locations included the ovary/testicle (2/64), swim bladder (2/64), pancreas (1/64), nasal (1/64), urogenital tract (1/64), body wall (1/64), and intestine (1/64).

Acknowledgements

The authors wish to acknowledge the Animal Health Care staff of the John G. Shedd Aquarium for their support of this project and the University of Illinois, Veterinary Diagnostic Laboratory's histology laboratory for excellent technical support.

References

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2.  Harshbarger JC, Spero PM, Wolcott NM. Neoplasms in wild bony fish from the marine ecosystem emphasizing environmental interactions. In: Couch J, Fournie J, editors: Pathobiology of Marine and Estuarine Organisms, Boca Raton, CRC Press, 1993; pp.157–176.

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4.  Sinnhuber RO, Lee DJ, Wales JH, Landers MK, Keyl AC. Dietary factors and hepatoma in rainbow trout (Salmo gairdneri) II. Cocarcinogenesis by cyclopropenoid fatty acids and the effect of gossypol and altered lipids on aflatoxin-induced liver cancer. Journal National Cancer Institute 1968; 41(6): 1293–1301.

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6.  Kagan RA, Pinkerton ME, Kinsel MJ. Neuronal embryonal tumors in fish. Veterinary Pathology 2010; 47(3): 553–559.