Tough to make money breeding fish. You have to have a market for the fish you breed. I've bred thousands of fish over the years. You may pay for the hobby, but you won't get rich. Fish that always sell - tropheus, catfish and anglefish.
If you're very stringent about your water quality, and have the necessary equipment on hand; then I would think either Altum Angelfish, or Zebra Plecos. They are some of the hardest fish to breed, but if you can pull it off; it's good money. They are two of south americas most sought after species in the aquarium trade, and even tank raised specimens demand a high price in most cases. I personally would target the zebra pleco, simply because they are listed as illegal to export from their native waters, as well as the fact that they are always in high demand.