Tumors and cancer in fish
Fish develop tumors and cancers, much like humans and other animals. However, sharks are a type of fish which never develops cancers.
Symptoms and Types
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. Treatment Most cancers and tumors found in fishes have no cure or treatment. Internal tumors or cancers are also not diagnosed until the advanced stages of the disease. And when it is identified early, the position and placement of the tumor often makes it inoperable. This is the main reason most fishes with tumors and cancers are terminated (euthanized).
However, there are some tumors which are treatable. For instance, gill tumor, which is caused by a thyroid problem, can be treated by placing the fish in water medicated with iodine.