A 10-year-old goldfish named George received life-saving surgery to remove a tumour from its head.

Yes, a goldfish.

Australian veterinarian Tristan Rich knocked George out with anaesthetic before inserting a tube from a bucket of water that contained a "maintenance level" of anaesthetic and oxygen into the fish's mouth so the water washed over George's gills during surgery.

The tumour, which meant George was unable to swim or eat properly, was removed and Rich had to put in four stitches to seal the wound, as well as use glue.

Soon after surgery, George "took a couple of breaths on his own and started swimming around."

"The surgery went swimmingly and George has now returned home with his loving owner," the Lort Smith Animal Hospital said on its Facebook page.

Rich told the Sydney Morning Herald George's owner was "quite attached" to the fish and agreed to surgery, for which she paid $200.