A 20-year-old goldfish, Bob, had been struggling to swim in his tank for a number of weeks after developing the lump on its fin, so the family took him to their local veterinarian and paid £200 to remove the lump. The operation lasted 30 minutes and it was so successful.
The vet said, he is doing brilliantly. They（the family）were really, really pleased because the goldfish is older than their children and considered part of the family.
To keep Bob alive during the operation, the vet fed anesthetic water into its mouth through a tube and used a tiny monitor to measure its heartbeat. She then cut out the tumor using a miniature pair of scissors and forceps.
"It’s pretty complicated because the organs of the fish are so small and they don’t have a massive volume of blood," she added.
The average lifespan of a goldfish kept in a tank is 5 to 10 years, with the vet confirming Bob was the oldest one she had ever operated on.
Source article: http://iservice.ltn.com.tw/Service/english/english.php?engno=1108864&day=2017-06-08