Betta

The Betta is a fish introduced in. It can be found in rivers from May to October (in the Northern Hemisphere), and it sells for 2,500 Bells. It appeared in during the Fishing Tourney: Terrarium event alongside Gourami and Crystal Red Shrimp.

Donating to the museum
As with all fish in, the Betta can be donated to the island's museum by talking to Blathers, the curator. He will say the following when given a Betta:

In
Once donated to the museum, the Betta can be found in the fish tank in the entrance room alongside the Angelfish and the Nibble Fish.

Real-world information
The betta, or Siamese fighting fish, is native to Southeast Asia. They lives in shallow bodies of water such as marshes or streams. Bettas are very territorial and aggressive, especially the males, and they may attack and possibly kill each other if kept in the same tank.