From Nookipedia, the Animal Crossing wiki
Donating to the Museum
After a nibble fish is donated, a sign in the museum will display information about this fish.
"The official name given to this warm-water-dwelling species of fish is "Garra rufa." They are omnivorous, as they both eat algae and scrape the skin off other fish. All you'd have to do to feed them is stick your hand in the tank; they would live off your dead skin. That's why they're called nibble fish. They exfoliate but don't have any teeth, so it doesn't hurt at all!"
Commonly known as doctor fish, Garra rufa are used in some methods of spa treatment, and have even been known to alleviate symptoms of psoriasis.
Names in other languages