Koi

The Koi is an fish that can be found in the river. It appears all year from 4PM to 9AM. When selling it to Re-Tail, the player will earn 4,000 Bells.

Location
The Koi is found in the river.

The Museum
The Koi can be donated to the museum. Upon doing so, the following text is given by Blathers:

"Though typically pale in color, these aquarium fish also can be found with rather beautiful patterns. This is all thanks to very selective breeding of carp with genetic mutations, allowing for diversity. No two koi have the exact same pattern and are popularly known as "swimming jewels" as a result. They can be sold for a very high price, depending on their coloring and pattern. If properly cared for, they can live for over 100 years, making them a staple for outdoor garden ponds."

Quote
Upon catching the fish, the player will say the following:

"I caught a koi! Can't play koi with me!"