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The Goldfish Gazette, Issue #102 Tumors in Goldfish
June 28, 2022

Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
June 2022
Issue #102

In This Issue
Tumors in Goldfish

As with all advanced animals, Goldfish can develop tumors both internally and externally, but it is the internal tumors that are the bigger problem.

Tumors In Goldfish

Internal Tumors

Internal tumors can go unnoticed until well advanced when the fish has swollen to a size and shape that is clearly not normal. They can often be misdiagnosed as fatty liver, egg impaction, dropsy, or simply a female ready to spawn.

The fish above has none of these conditions, it has an internal tumor called a Gonadal Sarcoma.

I know this for certain because two of the parents and a sibling have succumbed to this genetically inherited condition. I performed a necropsy on one of the parents which identified the tumor type.

This tumor seems more common in fancy varieties and as it is an inherited condition showing up in older fish, (the parents were 8 years old and the fish above is 5 years old) the breeder will only realize they have a problem after several years of breeding have passed.

Although the fish live several months or more depending on water temperature, this tumor is terminal. The fish will develop dropsy and balance problems in the final stages as the growing tumor compresses internal organs.

If a fish has a swollen belly, it isn't your breeding season, and the scales aren't raised, suspect an internal growth. An X-ray taken by your local vet is a useful tool to confirm a diagnosis.


Surgery is possible but finding a vet doctor capable of performing it would be the problem for most, and identifying the problem early is necessary for a successful surgery.

Ground-up apricot seeds have been touted as a possible cure, but I haven’t found them to be effective.

External Tumors

The most common external tumor found in Goldfish are Neurofibromas, nerve sheath tumors that cause localized skin and fin lumps that can grow very large, fall off, and then regrow.

They are benign tumors and do not cause the fish any distress, but they can become a problem if they get so large as to hinder swimming.


Total removal by surgery usually isn’t possible if the tumor is located on the body because the tumors can be quite deeply embedded, but it is worth doing if the growth is hindering swimming.

Carp pox

Carp pox is often misidentified as tumors as they look similar to Neurofibromas but usually, there are multiple growths present.

Initially, Carp pox shows as milky, waxy lesions on the skin which are raised and smooth in appearance.

It is caused by the herpesvirus-1 affecting the fish’s skin by causing abnormal skin cell production. There is no cure and the fish is believed to be infected for life, but the condition is rarely fatal.

Having said that, lesions covering the gills or mouth can hinder breathing or feeding.

This condition is most prevalent during low water temperatures in winter and early spring, probably when fish immune systems are at their lowest.

In severe cases, the infection diminishes the fish's immunity, leaves the lesion-filled area prone to secondary infection by bacteria, and the growth of the fish is affected.


The condition reduces as water temperatures increase so for any fish suffering from Carp pox I would increase the water temperature and add salt to the water to help boost its immune system.

Comments? Ideas? Feedback? I'd love to hear from you. Just reply to this e-zine and tell me what you think, or what topics you want to be covered.

Next Month's Topic

Water change dangers

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