What is this lump on my goldfish?

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Dr Peter Burgess helps a reader who is worried about a lump he has found on his goldfish.

Q) I have two fancy goldfish: a red Ryukin and a calico Fantail. The Ryukin has developed a lump on one side, although it seems fine otherwise. The Fantail, which you can also see in the photo I’ve sent, spends most of its time sitting on the bottom, just coming up to the surface to feed. Both fish feed well and water parameters are spot on. Please could you advise?

IAN MITCHELL, VIA EMAIL

A) DR PETER BURGESS REPLIES: Looking at the photo, your Ryukin goldfish appears to have a skin growth, possibly a type of tumour known as a fibroma.

Skin fibromas are fairly common on goldfish. Over the years, I have observed them develop on a few of my own goldfish, so a fibroma is my ‘best-guess’ diagnosis. To be absolutely sure it would be necessary to take a small sample (biopsy) of the growth and have it examined under the microscope by a fish pathologist — although I’m not suggesting that you need to do this.

Fibromas typically develop slowly over weeks or months, and some may eventually reach the size of a grape, sometimes larger. It’s possible that your affected fish may develop one or two (rarely many) additional fibromas in due course, though in most cases we see just one.

Fortunately, these types of skin tumour are generally harmless (one exception is when they arise near the fi sh’s eyes, gills, vent, or mouth and begin to smother these organs as they enlarge). Also, they are non-infectious, hence won’t spread to your other goldfish. On the downside, there are no chemical treatments to cure fi bromas, and there is nothing you can or should do. Chances are that your fi sh will live an otherwise healthy life, but obviously keep a regular check on its health, as you would for any other fish in your care.

As for the other goldfish that sits on the bottom much of the time, then this could be due to a swimbladder problem that’s caused the fish to lose its neutral buoyancy, making it sink. Unfortunately, these ‘man-made’, stumpy-bodied goldfish varieties are prone to swimbladder problems. You say it is feeding, so that’s a good sign. Ensure you don’t have too strong a water flow in the aquarium as these non-streamlined fish aren’t strong swimmers and may rest somewhere in the tank where the water current is less powerful.