Quick story about the totally inappropriate way to deal with fish breeding.
A good friend of mine had a 50g breeder; the same tank I now have. He stocked it with six Brichardi. Interesting chchlids from Lake Tanganyika. They're aggressive as hell to other species, but get along swell with each other. They're popular because they're so social-minded and they tend to each others fry, and set up a hierarchy for raising the youngsters. His six turned into a hundred, and for a while he would sell off the excess for supplies, but this gets to be a PITA. Eventually he just decides to just leave them alone figuring they'll work it all out. Filters, accidents, aggression, natural selection; it never gets too far out of hand. He gets a thriving community that lasts for 15 years or so. Then he starts to notice that they're mutating. A side effect of starting with a small gene pool is that it doesn't take too many generations to start seeing some weird shit. He wound up with a completely different fish than what he started with. Similar, but with big protruding jaws. Unfortunately, the mutations didn't prove to be advantageous to the species, so it never really propagated too far. While the mutants did actually outlast, outwit and outplay the norms, they didn't prove successful enough to continue on and slowly died off. Eventually it got down to two mongoloid looking fish, who didn't really pay much attention to each other. Eventually, one of them killed the other out of boredom, and then jumped over board. Then he gave the tank to me.
Moralistic fish-keepers are full of things you're supposed to do to keep this from happening. Personally, I thought it was a god damned hoot. It was a wonderful study of natural selection in a 20 year microcosm. Frankly, this was far more entertaining than the hierarchical nursery. And best of all, it took almost no effort whatsoever.