NON-INFECTIOUS DISEASES Neoplasia (Tumors)

I. Causative Agent and Disease transmission does not occur. Generally, Tumors or neoplasms are tissue neoplastic growths are spontaneous growths of abnormal cells that prolifer- within an individual due to congenital ate uncontrollably. In bony fishes, neo- malformation, age or genetic predisposi- plasms of the connective tissues, such tion but could also be caused by environ- as fibroma and fibrosarcoma, are most mental conditions. common. Fish develop neoplasia or can- cer in much the same way as do higher V. Diagnosis/Classifcation animals. Known and suspected factors Definitive diagnosis is made by contributing to neoplasia in fish include observing the abnormal cells using his- viruses, environmental chemicals topathological methods. Neoplasms are (carcinogens), repeated physical trauma, classified according to the cell or tissue hormones, age, sex, genetic predisposi- of origin and are further grouped based tion and immunological competence of on benign or malignant characteristics. the host. Benign tumors are often well-differen- tiated, grow slowly, are well circum- II. Host Species scribed without invading surrounding normal tissue and do not metastasize. All teleost fishes in any part of the Most benign neoplasms are not usually world could potentially develop neopla- life threatening and often end in the sia. For unknown reasons cancer has suffix “oma”. Exceptions are benign neo- been rare in cartilaginous fishes such as plasms of the brain and some endocrine sharks and rays. organs that can be life threatening due to their location and deleterious physiologi- III. Clinical Signs cal effects on the host. Malignant tumors Neoplasms usually become apparent are often not well differentiated, may by gross observation of an external or grow rapidly, infiltrate normal tissues internal swelling, lump, or formation of and tend to metastasize. The names of an abnormal tissue growth. these neoplasms are often preceded by the word “malignant” or with the suf- IV. Transmission fixes “sarcoma” or “carcinoma”. Types Except for neoplasia caused by of cancer in fish include the following: infectious viruses, horizontal fish to fish

TISSUE TYPE BENIGN TUMORS MALIGNANT TUMORS epithelial papilloma epithelial carcinoma adenoma adenocarcinoma mesenchymal fibroma – connective tissue fibrosarcoma leiomyoma – smooth muscle leiomyosarcoma rhabdomyoma – striated muscle rhabdomyosarcoma lipoma – fat liposarcoma chondroma – cartilage chondrosarcoma osteoma – bone osteosarcoma hematopoietic lymphoma lymphosarcoma blood vessels hemangioma hemangiosarcoma neural – nerve cell schwannoma glioma, astrocytoma pigment erythrophoroma malignant melanoma embryonal nephroblastoma -

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VI. Prognosis for Host VII. Human Health Signifcance Prognosis for fish having neoplasms Although aesthetically disturb- depends on the type of tumor and ing, there are no direct human health whether the lesion is benign or malig- concerns associated with neoplasia in nant. Benign tumors are usually not fish. Neoplasia is generally a rare event life threatening. Malignant tumors can affecting one fish in several thousand. cause mortality if growth is rapid and Should tumors occur more frequently in interferes with normal organ functions. a population of fish, an indirect human health concern would be whether the cause is linked to environmental con- tamination.

Fibroma, on right dorsal anterior fank of a sockeye salmon.

Liposarcoma on the abdomen of a whitefsh.

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Left: Cut surface of a liposarcoma on the back of a quillback rockfsh; Right: Thymic lymphosarcoma (arrow) in branchial cavity of a sockeye salmon.

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Left: Fibrosarcoma (arrow) infltrating the muscle tissue from the body wall in a salmon; Right: Pedunculated papilloma on the back of a coho salmon.

Left: Rhabdomyosarcoma (green) in the musculature of a Pacifc halibut; Right: Black melanoma on the head of a chum salmon; Inset: Sockeye: when cut, melanomas can exude a black tarry fuid containing melanin pigment that stains surfaces, (photo: Scott Albert).

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NON-INFECTIOUS DISEASES 

Left: Ameloblastoma from odontogenic epithelium of teeth in king salmon causing thickened maxillaries (arrow); Right: Fibrosarcoma in left posterior body wall of sockeye salmon.

Left: Multifocal dermal fbrosarcoma in skin of pink salmon; Right: Prickle cell carcinoma of the epidermis in a sablefsh.

Left: Fibrosarcoma of the skin in a sheefsh; Right: Unidentifed reddish neoplasm in anal area of a northern pike heavily infested with leeches.

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