You can enjoy fish-keeping for a lifetime without ever breeding your fish. But breeding adds a new dimension to the hobby. To breed fish requires more time and attention. The rewards include a deeper knowledge of fish species and the fascinating observation of the egg laying, fry, and parenting behavior (or lack thereof) in the breeding pair.
Fish breed in two basic ways. Some, like cichlids, lay eggs, and egg-layers are usually more challenging to breed. Others, such as swordtails and guppies, bear live young and are more prolific parents. They are also easier to breed.
There's a lot of fun in breeding, but unfortunately, little profit: fish stores usually have more than enough stock, so most don't buy fry, though at some stores, they will accept fry in trade or for store credit. Breeders who join an aquarium club may find fellow members willing to buy or swap for fry.