Pebbles is a 20-year-old koi.

The pet fish, unfortunately, had to undergo surgery to remove a large mass that was invading her fin.

Veterinarians from HousePaws Mobile Veterinary Service sedated the koi, and kept her asleep by squirting sedative-treated water into her gills.

After the mass was removed, Pebbles received pain and antibiotic injections.

The mass will be sent for a biopsy, or an examination of the tissue to discover its cause.

But according to the United States-based veterinarians, Pebbles' partner, Chase, appeared to be "really upset" when she was away from the pond.

When Pebbles returned, Chase reportedly positioned himself right next to her, while her sedative was wearing off.

The vets managed to capture the two fish together:

Sweet.

Several online sites have indicated that koi fish are generally docile, sociable creatures that enjoy living in pairs or in groups.

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Top image via HousePaws Mobile Veterinary Service/Facebook