There are a lot of species of fish, and a lot of different ways to breed them... As the first person mentioned, male and female guppies will get it on in a puddle. Any livebearers are the easiest fish to breed. A male and a few females, and you have fry. Most will eat their fry though, so you should separate them. Idk what beats are though, I always thought those were vegetables, not fish. If he meant Bettas, he's sadly mistaken. Bettas are much harder to breed than most fish.