When I was growing up, my sister was fascinated by fish and even had a small fish farm happening in her bedroom. Though she never turned it into a business, it would have been a good one if she´d chosen the right type of fish.
Fish breeding is not terribly difficult, if you have a good setup and understanding of how things work. In general, you will need at least two or three fish tanks, one for breeding, one for the babies and another for growing young ones who might pose a threat to smaller babies. If you have more than one species, you´ll need more tanks.
This can be an ideal work at home business for moms because kids love to watch fish. Since the fish are inside tanks, it´s a bit more difficult to accidentally squish them or teach them bad habits, as well. For a decent sized business, you will probably want to dedicate an entire room to fish breeding.
Before starting your fish breeding business, it´s a good idea to check out the market. Talk to some pet shops and find out what they are looking for, what sells best, etc. You will want to talk to more than one shop and also get a feel for whether or not they are open to new suppliers. Then you can begin your breeding program.
If fish breeding sounds like an interesting work at home business to you, you can learn more at this Fish Breeding FAQ.