San Diego Zoo veterinarians removed cancerous masses from a 35-year-old koi last month, the zoo said Tuesday.

Wildlife specialists noticed a skin mass on the koi as the fish was swimming in its pond at the zoo’s Terrace Garden.

The fish was moved May 15 to a tank and transported to the zoo’s veterinary hospital, where it was placed on a specially built table for fish exams.

“There were three skin masses removed from the koi,” said Ben Nevitt, senior veterinarian. “The concern was that the masses could become ulcerated and affect deeper tissue. Upon examining the fish, the masses seemed to only affect the scales in the area and not underlying skin, so the mass removals were pretty straightforward.”

San Diego Zoo veterinarians remove masses from a koi at zoo’s veterinary hospital. Photo by Ken Bohn, San Diego Zoo Global

Nevitt said the masses were diagnosed as spindle cell carcinoma, which may return in those areas, but should not spread to the rest of the body.

The koi was returned to its 18,500-gallon pond the same day as the medical procedure. It is currently eating normally, and the surgery sites have all healed well. The koi will be monitored closely for any recurrence of the masses.

Koi operations are not unknown.

In October 2018, UC Davis’ Aquatic Animal Health Unit of the Companion Exotic Animal Medicine and Surgery Service removed a softball-sized gonadal tumor from a 6-year-old koi named Madonna. The tumor was nearly half her 5-pound body weight.

Last October, a koi named Bubbles underwent a 10-minute surgery to remove a potentially fatal tumor. James Cook University veterinarians did the operation.

“We wanted to see the fish survive,” said owner Michael Dare in Townsville, Australia. The procedure cost around $300, but its “survival is more important than cost.”

And on California’s Central Coast, 7-year-old Aquatic Veterinary Services says: “Fish do not receive the same respect as a cat, dog or horse. … Fish deserve all the same care and consideration as your other pets, and our service is your one-stop shop.”

Koi are ornamental varieties of domesticated common carp that originated in Japan. At the Balboa Park zoo, they live in outdoor ponds with clean, oxygenated water and plenty of shade “as they are susceptible to sunburn,” the zoo said.

“Koi are culturally significant, and represent love and friendship in Japan,” the zoo said. “Some koi have been known to live more than 200 years.”

The zoo said its koi patient was anesthetized, with water continuously run over its gills to allow it to breathe, while a veterinarian safely examined the fish and removed the masses.

After being closed to guests since mid-March, the San Diego Zoo and the San Diego Zoo Safari Park reopened to the public on Saturday, ending the first major closure in the organization’s 103-year history.

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