Monty, a beloved five-year-old family pet, had multiple tumours behind its left eye which had spread through its back.
A team of vets from Highcroft Veterinary Group and Bristol Zoo carried out the 45-minute operation, which saw the tiny fish placed in water soluble anaesthetic.
Throughout the £200 operation, it had oxygenated water flushed through its gills and eye.
It went swimmingly and the beloved pet is recovering at home in Bristol.
Sonya Miles, exotics veterinary surgeon at Highcroft Veterinary Group, said: “I assisted Bristol Zoo Vet, Michelle Barrows with Monty’s surgery which took just over 45 minutes in total.
“He was a brilliant patient and the surgery went very smoothly from start to finish.
“His owners are extremely dedicated and they paid to make sure he had a better quality of life.
SWNSMontyRecovering: Monty, a beloved five-year-old family pet
“We don’t perform surgery on goldfish very often but we are seeing a definite increase in veterinary treatment in fish generally.
“Monty is doing exceptionally well at home and is acting as if nothing has even happened.”
