Fishes develop tumors and cancers, much like humans and other animals. However, sharks are a type of fish which never develops cancers.
Most tumors are seen as bumps or lumps under the fish's skin. But the location and signs of the tumor can be different for each fish, and depend greatly on the type of tumor. Unfortunately, internal tumors or cancers display symptoms once it has become to late to save the fish. Also, the fish’s ability to eat and swim will be affected, causing a rapid decline in its health.
Koi fishes usually get tumors in the reproductive organs. They will have swollen abdomens and the illness can become terminal. Conversely, goldfish are susceptible to fibroma tumors and sarcoma cancers. While Gypsy-swordtail fishes, generally develop skin cancer (malignant melanoma).
Another type of tumor is found in the gills. It causes the fish to be unable to close its gills, and is due to a thyroid dysfunction. Despite its seriousness, the tumor has a good success rate when it is treated.
Most fishes get tumors or cancers due to genetic predisposition. Some fishes, however, can get tumors or cancers from a viral infection.
A type of neoplasm that occurs in connective tissue
Something that becomes worse or life threatening as it spreads