I would say no. Really, the only fish suitable for a tank that small is a betta. And, even then, that's a bit small for a betta. In the 2.5 you could also try shrimp or snails. However, I would say you could probably keep one in a five gallon if you kept up on the maintnance. I am not 100% sure, so I would wait for a bit of input from others.