Ranchu goldfish

The Ranchu Goldfish is a rare pond fish in the introduced in. It also appears in as an event fish that was available during Fishing Tourney: Elegant Aquarium in August 2020.

In
When asked about the fish, Blathers will say the following:

"The ranchu goldfish is a charming relative of the goldfish with a bumpy head and stout, round body. They have ordinary heads when born, but develop impressive rectangular heads after about three years. Supposedly their head shape changes depending of factors like the size of their tank... So ranchu goldfish enthusiasts aim to raise perfectly shaped specimens and work hard to achieve this. Of course, no one asks the ranchu goldfish themselves what shape they want their heads to be..."

The Goldfish can be found in the tank immediately to the right of the entrance to the fish section of the museum.

Real-world information
The Ranchu, (jap.: Katakana: ランチュウ; Kanji: 蘭鋳, 蘭虫 or 卵虫, literally "Dutch worm") is a hooded variety of fancy goldfish developed in Japan. It is referred to as the "king of goldfish" by the Japanese.

The modern-day ranchu is a Japanese development of the lionhead. They are the direct outcome of crossbreeding experiments of different Chinese lionhead specimens.