Get a picture of it lolit looks like a tiny bristlenose pleco. Its maybe a 1/4 of an inch long. The only other fish it might be is a corydora fry but it just doesn't look like it.
a betta, zebra dainos and neon tetras. It's actually my daughter's tank that which ends up with odds and ends from my other tanks.
If you have two bettas then i'd guess it could be betta fry?