Tumors in Goldfish
In the past six months I've received more than the usual amount of e-mails about goldfish tumors.
Some Goldfish will develop tumors. Goldfish Collectors can not tell if the tumor is cancerous or not without the help of a good fish Vet. In rare cases some tumors can transmit TB to humans.That's why it's so important not to place your hands in a goldfish aquarium if you have a cut or open skin on your hands.
Some goldfish will show no signs of stress with a tumor, others will lose weight no matter how much they eat, some will become inactive and stop eating.
There is no treatment for tumors. I never kept a goldfish with a tumor because I didn't know if the goldfish was suffering with pain and I did not want to take any chances of contracting anything from the tumor. However, whether you keep a fish in that condition is your call.
Here is a Goldfish with extreme tumors: