Field studies[1](Bills et al 2012) show this group, not unlike other killies, is still undergoing diversification.

[1] "A SURVEY OF THE FISHES OF UPPER OKAVANGO RIVER SYSTEM IN ANGOLA
SAIAB Investigational Report No. 73.
Roger Bills, Paul Skelton and Francisco Almeida

Poeciliidae – Topminnows
The known species from the Okavango delta are Aplocheilichthys johnstoni, A. katangae, A. hutereaui and an undescribed species Aplocheilichthys sp. ‘pygmy’. All are abundant in suitable habitats of the delta and each species appears to have clear habitat preferences. Unexpectedly Aplocheilichthys were rare during the May 2012 Angolan survey. They were not collected at all sites and generally when they were collected they were not abundant. The species/forms encountered were also different from those known from lower parts of the system. Aplocheilichthys hutereaui was absent, Aplocheilichthys sp. ‘pygmy’ was collected at only 1-2 swampy floodplain sites (typical habitat). The two most common species were similar to A. johnstoni and A. katangae but both seemed to differ in colour patterns to specimens from the Okavango delta.

Not all bar-code results are back yet but results so far plus our morphological examinations indicate there is greater diversity than previously recognized within the Okavango system. New species include the known, undescribed Aplocheilichthys sp. ‘pygmy’ and then one Aplocheilichthys katangae-like species and one A. johnstoni-like species. Additional collections of these with more careful field examination and targeted genetic sampling will help to hone our determinations within this group. Interestingly there appear to be considerable genetic differences between morphologically similar groups across the broader Zambezian region indicating a complex of species"