Many fish that are closely related can interbreed but can still be classified as separate species. That being said, there have been so many advances in cichlid classification over the last 15 to 20 years, many fish that we believed were separate species are now being shown to be regional variations of the same fish. Also, some we thought were regional variations are being shown to be different enough to class as separate species.
For example, there is great debate and has been for a few years now regarding Frontosa. There is a Seven-striped Front that was always considered to be a regional variation, but is now considered by many scientists to have enough differences in scale pattern and other physiological markers to be considered a sub-species of Front.
If you look back on cichlid species lists from 10 or 20 years ago, or even older, almost all SA/CA cichlids had the family name Cichlasoma. That name is almost completely gone now, with most cichlids classified into more descriptive and more accurate families. There is also a lot of family name swapping going on. Take JD's as an example. They've been Cichlasoma, Heros and Nandopis recently.... and thats only the ones that I can remember off the top of my head
