The koi was taken, via a tank, to the zoo’s veterinary hospital, where a veterinarian examined the fish’s masses on a table specially built for aquatic animals.

“The concern was that the masses could become ulcerated and affect deeper tissue,” Dr. Ben Nevitt, the zoo’s senior veterinarian, explained in the release. “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.”

A veterinarian removed the masses while the koi was under anesthesia; meanwhile, water was continuously run over the fish’s gills, allowing it to breathe.