What causes tumors on goldfish?

Tumors in goldfish can be caused by various factors, including viral infections, genetic predisposition, environmental stressors, and poor water quality. Certain viruses, such as the carp pox virus, can lead to the development of tumors. Additionally, prolonged exposure to harmful chemicals or poor tank conditions can weaken the fish's immune system, making them more susceptible to tumor formation. Regular monitoring of water quality and maintaining a healthy environment can help reduce the risk of tumors in goldfish.