The male on the left looks like a half-black (dark colored body) with a yellow/orange tail?? If so, it is probably a guppy. However, it is hard to tell from the photo. Either way, fishkeeping is good.
We have a 10-gallon aquarium at my work with guppies that have been in there mor ethan 10 years. Not the same guppies, of course, but descendents. The tank seems to maintain a stable population, more or less.