Scheel's 1960 masterwork on Rivulins suggested Aplocheilus was the basal stock to all Rivulins, that is, all old world killifish except the lampeyes were felt to have evolved from these. Decades later with and because of DNA evidence we now know that Pachypanchax a far more primitive fish, actually the foundation stock for half of all Killifish.
These are the only Aplocheilids found outside of Africa or the Americas; then range from India to Borneo.
Every fish on this page makes a fine aquarium fish
Pachypanchax playfairi and what was thought to be P. omolonotus were imported in the 1900s but by the 1970s it became obvious that what we were calling P. omolonotuswas not, the fish from Nosy Be, Madagascar previously referred to P. omolonotus was renamed P. arnoulti. Since then a good number of new forms have been found ranging from excellent to superb aquarium fish all of which are endangered some of which are very critically so.
All are found off the east coast of Africa. P.playfairi is the sole freshwater fish on the Seychelle Island while the rest are all found only on Madagascar.
Notice the similarity between Aplocheilus and this specimen of P. arnoulti:
