Neoplasia in Fish: Types, Clinical Signs, Diagnosis, and Prognosis | Study notes Clinical Psychology

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NON-INFECTIOUS DISEASES

Neoplasia (Tumors)

I. Causative Agent and Disease

Tumors or neoplasms are tissue

growths of abnor mal cells that prolifer-

ate uncontrollably. In bony fishes, neo-

plasms of the connective tissues, such

as fibroma and fibrosa rcoma, are most

common. Fish develop neoplasia or can-

cer in much the same way as do higher

animals. K nown and suspected factors

contribut ing to neoplasia in fish i nclude

viruses, environmental chemicals

(carcinogens), repeated physical trauma,

hormones, age, sex, genetic predisposi-

tion and immunological competence of

the host.

II. Host Species

All teleost fishes i n any part of the

world could potentially develop neopla-

sia. For unknown reasons cancer has

been rare i n cartilaginous fishes such as

sharks and rays.

III. Clinical Signs

Neoplasms usua lly become appare nt

by gross observation of an external or

internal swelling, lump, or formation of

an abnormal tissue growth.

IV. Transmission

Except for neoplasia caused by

infectious v iruses, horizonta l fish to fish

transmission does not occur. Generally,

neoplastic growths are spontaneous

within an individual due to congenital

malformation, age or genetic predisposi-

tion but could also be caused by environ-

mental conditions.

V. Diagnosis/Classifcation

Definitive diag nosis is made by

observing the abnormal cells using his-

topathological metho ds. Neoplasms are

classified accord ing to the cell or t issue

of origin and are further grouped based

on benign or malignant characteristics.

Benign tu mors are ofte n well-differen-

tiated, grow slowly, are well circum-

scribed without invading su rrounding

normal tis sue and do not metast asize.

Most benign neoplasms are not usually

life threatening and often end in the

suffix “oma”. Exceptions are benign neo-

plasms of the brain and some endocrine

organs that can be life threatening due to

their location and deleterious physiologi-

cal effects on the host. Ma lignant tu mors

are often not well di fferentiated, m ay

grow rapidly, infilt rate normal t issues

and tend to metastasize. T he names of

these neoplasms are often preceded by

the word “maligna nt” or with the s uf-

fixes “sarcoma” or “carcinoma”. Types

of cancer in fish include the following:

TISSUE TYPE BENIGN TUMORS MALIGNANT TUMORS

epithelial papilloma epithelial ca rcinoma

adenoma adenocarcinoma

mesenchyma l fibroma – conne ctive tissue fibrosarcom a

leiomyoma – smooth mus cle leiomyosarcoma

rhabdomyoma – st riated muscle rhabdomyosarc oma

lipoma – fat liposarcoma

chondroma – cartilage chondrosarcoma

osteoma – bone osteosar coma

hematopoietic lymphoma lymphosarcoma

blood vessels hemangioma hemangios arcoma

neural – ner ve cell schwa nnoma glioma , astrocytoma

pigment eryth rophoroma maligna nt melanoma

embryonal n ephroblast oma -

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Neoplasia (Tumors)

I. Causative Agent and Disease Tumors or neoplasms are tissue growths of abnormal cells that prolifer- ate uncontrollably. In bony fishes, neo- plasms of the connective tissues, such as fibroma and fibrosarcoma, are most common. Fish develop neoplasia or can- cer in much the same way as do higher animals. Known and suspected factors contributing to neoplasia in fish include viruses, environmental chemicals (carcinogens), repeated physical trauma, hormones, age, sex, genetic predisposi- tion and immunological competence of the host.

II. Host Species All teleost fishes in any part of the world could potentially develop neopla- sia. For unknown reasons cancer has been rare in cartilaginous fishes such as sharks and rays.

III. Clinical Signs Neoplasms usually become apparent by gross observation of an external or internal swelling, lump, or formation of an abnormal tissue growth.

IV. Transmission Except for neoplasia caused by infectious viruses, horizontal fish to fish

transmission does not occur. Generally, neoplastic growths are spontaneous within an individual due to congenital malformation, age or genetic predisposi- tion but could also be caused by environ- mental conditions.

V. Diagnosis/Classifcation Definitive diagnosis is made by observing the abnormal cells using his- topathological methods. Neoplasms are classified according to the cell or tissue of origin and are further grouped based on benign or malignant characteristics. Benign tumors are often well-differen- tiated, grow slowly, are well circum- scribed without invading surrounding normal tissue and do not metastasize. Most benign neoplasms are not usually life threatening and often end in the suffix “oma”. Exceptions are benign neo- plasms of the brain and some endocrine organs that can be life threatening due to their location and deleterious physiologi- cal effects on the host. Malignant tumors are often not well differentiated, may grow rapidly, infiltrate normal tissues and tend to metastasize. The names of these neoplasms are often preceded by the word “malignant” or with the suf- fixes “sarcoma” or “carcinoma”. Types of cancer in fish include the following:

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 -

VI. Prognosis for Host Prognosis for fish having neoplasms depends on the type of tumor and whether the lesion is benign or malig- nant. Benign tumors are usually not life threatening. Malignant tumors can cause mortality if growth is rapid and interferes with normal organ functions.

VII. Human Health Signifcance Although aesthetically disturb- ing, there are no direct human health concerns associated with neoplasia in fish. Neoplasia is generally a rare event affecting one fish in several thousand. Should tumors occur more frequently in 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.

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.

Neoplasia in Fish: Types, Clinical Signs, Diagnosis, and Prognosis, Study notes of Clinical Psychology

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Neoplasia (Tumors)