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Fish Neoplasms
by Robert B. Moeller Jr., DVM

California Animal Health and Food Safety Laboratory System
University of California
 

Melanoma in Platyfish/Swordtail hybrids

Unique invasive melanoma that occurs in the offspring from F1 hybrid platyfish/swordtail with the spotting traits that are crossed with swordtails. F1 hybrids with the spotting trait develop premelanosomes. F1 X swordtail cross will produce frank melanomas. The reason for these melanomas is believed to be due to enhancement of the macromelanophore gene due to a deficiency of modifier genes that leads first to melanosis and finally to invasive melanomas.

Hepatoma and hepatocellular carcinoma in rainbow trout

The fry of rainbow trout are very susceptible to aflatoxins in the feed. These hepatic neoplasms are associated with the ingestion of aflatoxins in the feed. Acute aflatoxicosis causes acute massive liver necrosis with bile duct proliferation.

Stomatopapilloma of eels (Cauliflower disease)

These are large firm cauliflower like masses that are attached to the mouth. Tumors tend to proliferate in the summer and degenerate in the winter. A birnavirus, similar to infectious pancreatic necrosis virus, has been reported to have been isolated from the affected eel (Anguilla anguilla). However, initiation of the tumor with cell free extracts has been unsuccessful.

Papilloma of the Brown bullhead

Papillomas are common in the brown bullhead with occurrence on the head and lip. Viral particles have been observed ultrastructurally in the papillomas, but a virus has not been isolated. Some of these papillomas may progress and become locally invasive squamous cell carcinomas.

Lip Fibroma (Fibropapilloma) of Angel Fish

Tumor of the mucocutaneous junction of the lip near the midline. Adult female fish are the only effected fish. Tumors begin as small white vesicles that enlarge over several weeks. The tumors are firm, lobulated, and elevate the epidermis. On cut sections, the tumors are white with some having cavernous centers filled with clear fluid.

Histologically, the tumors consist of dense fibrovascular connective tissue arranged in whorls, streams and bundles and covered by a thick stratified squamous epithelium. Cause is unknown. A type "A" retrovirus has been isolated from affected tissue. Laboratory transmission of the disease to other fish has not occurred.

Dermal Fibrosarcomas of Walleye pike

Fibrosarcomas are a common neoplasm affecting a large variety of fish. Dermal fibrosarcomas of Walleye pike arise in the dermis and cause multifocal nodules over the entire body. They can be very large and locally invasive. A type-C retrovirus has been associated with this disease. Occasionally, this neoplasm has also been associated with a herpesvirus induced epidermal hyperplasia or lymphocystis disease.

Lymphosarcoma of Pike

This is an epizootic condition in northern pike and muskellunge in certain regions (i.e. Lake Ontario). The lesion develops as a purple ulcerative cutaneous mass on the head, mouth and flank with invasion into the adjacent muscle and metastasis to spleen, liver and kidney. A type-C Retrovirus is believed to be the cause of this disease.

Schwannoma/Neurofibromas of the bicolored damselfish (Damselfish Neurofibromatosis DNF)

Neurofibromas have been reported in numerous species of fish. The bicolored damselfish has gained notoriety in that some of these fish develop multiple cutaneous schwannomas. This neoplasm is believed to possibly represent an animal model for von Recklinghausen Neurofibromatosis (NF type 1) in man. The similarities and differences between these two diseases are as follows: The primary lesion in both NF type 1 and DNF are neurofibromas, many of which are plexiform in nature. The fish tumors are often malignant. DNF the pigment lesions can be neoplastic and quite invasive, while the cafe au lait spots of NF type 1 are benign. NF type 1 appears to be genetically transmitted while DFN appears to be horizontally transmitted.

Plasmacytoid Leukemia (Marine anemia) of Chinook salmon

Plasmacytoid leukemia virus is observed in farmed raised Chinook salmon (Experimentally in Sockeye, Coho and Atlantic salmon). It is believed to be caused by a retrovirus (Salmon leukemia virus). Affected fish become lethargic, have dark skin, pale gills (anemia), and exophthalmus. The spleen, kidney, and retrobulbar tissues are enlarged and mottled. Petechial hemorrhage of the serosa is common. Infiltration of the liver, spleen, and kidneys with plasmablastic cells is noted. Plasmablast have a slightly lobulated nucleus with a central nucleoli.

REFERENCES

1. Roberts R.J: Fish Pathology, Bailliere Tindall, London, Second edition, 1989.

2. Ferguson H.W.: Systemic Pathology of Fish, Iowa State Press, Ames, Iowa, 1989.

3. Anderson B.G.: Atlas of Trout Histology, Wyoming Department of Fish and Game, 1974.

4. Fox J.C.: Laboratory Animal Medicine, Academic Press, 1984.

5. Magaki G., Rebelin W.E.: The Pathology of Fishes, The University of Wisconsin Press, 1975.

6. Wolf K.: Fish Viruses and Fish Viral Diseases, Cornell University Press, London 1988.

7. Tucker C.S.: Channel Catfish Culture, Elsevier Science Publishers, Amsterdam, 1985.

8. Principal Diseases of Farm Raised Catfish, Southern Cooperative Series Bulletin No 225, 1985.

9. Wales J.H.: Microscopic Anatomy of Salmonids. An Atlas, United States Department of the Interior, Resource Publication 150, 1983.

10. Grizzle J.M.: Anatomy and Histology of the Channel Catfish, Auburn Printing Co, 1976.

11. Reichenbach-Klinke H. H.: Fish Pathology, T.F.H. Publications, Inc. Neptune City, NJ. 1973.

12. Stoskopf, M.K.: Fish Medicine, W.B. Saunders Co. 1993.

13. DeTolla, L.J., Srinivas, S.: "Guidelines for the Care and Use of Fish in Research". Institute of Laboratory Animal Resourses Journal. Vol 37:4(1995), pp 159-173.

14. Kane, A.J., Gonzalez, J. F., Reimschuessel, R: "Fish and Amphibian Models Used in Laboratory Research". Laboratory Animal. Vol 25:6(1996), pp 33-38.

15. Lewbart G.A. Self-Assesment Color Review of Ornamental Fish, Iowa State Press,1998.

16. Bruno D.W., Poppe T.T., A color atlas of Salmonid Diseases. Academic press, 1996.

 

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