I've heard that some synodontis catfish will breed in captivity. This has been done in tanks with 15+ catfish in them, and I would imagine that you couldn't keep them in there after they lay eggs, so you would have to spend hours trying to catch them all if you wanted to raise the babies. If you want something easier, apple snails are great breeders. Corydoras breed somewhat easily. If you want something bigger 10-12 inches, silver needle-nose gar have bred in captivity.