Neon tetra

The Neon Tetra (ネオンテトラ, neon tetora) is a tiny fish found in the river between the months of April and November between 9am and 4pm. It is the smallest fish in the. It is introduced in and it returns in.

City Folk
Upon the player's donating the fish to the Museum, Blathers will say the following

"That metallic blue body! Hoo, that crimson tail! That pristine white belly! ...Now, THIS is what I call a tropical fish! No wonder this fish has the word "neon" in its name, eh wot? One of these should liven up the museum nicely!"

It can be found in the small tank to the left with the Goldfish and Popeyed Goldfish in City Folk.

New Leaf
"Neon tetras get their name from the beautiful blue metallic line on their bodies. Although they're shy, gentle fish, surprisingly they're related to the piranha, though very distantly. They have very sharp and narrow teeth, an odd contrast to their beauty. They are delicate fish who tend to be very sensitive to the cleanliness and temperature of water."

Encyclopedia Information
Once caught, the Neon Tetra has the following information about it in the Fish Encyclopedia:

Further Information
Neon tetras are native to backwater and clear water streams in southeastern Columbia, eastern Peru and western Brazil, living in the Amazon river. Neon tetras are a popular aquarium fish, mainly because of its appealing coloration. It has a light-blue back that meets a silver-white abdomen, with a red and blue stripe in between them. It is however, transparent. During the night, when the neon tetra is inactive, it loses its red and blue stripe, which turns silver. There is a slight difference between male and female neon tetras. The males have a straight red-blue stripe while females have a slightly crooked stripe, because of their rounder body shape. Neon tetras can be afflicted by "Neon Tetra Disease" (or NTD), which is incurable. It involves the loss of coloration in the bodies as well as restlessness.