Cynopoecilus Regan 1912 was erected in the description of C. melanotaenia. Myers (1952) saw Cynopoecilus as a subgenus of Cynolebias, and later Parenti (1981) placed C. melanoaenia in Cynolebias. But Costa, Lacerda and Brasil (1989), and later Costa (1990b), followed Regan by resurrecting Cynopoecilus to generic status.
The genus now contains five species, mostly on the basis of osteological data. Meristic differences between the components are slight, and could merely represent color variations of Cynopoecilus melanotaenia. 
There is a strong relationship between Cynopoecilus and Leptolebias. Also there is a clear relationship with Campellolebias. They live not only in the same types of habitat, but also share a remarkable feature (in Rivulids), having a gonopodium-like apparatus at the insertion of the anal fin. This structure, however, differs from that of Campellolebias, in which it is separated from the fin itself, and is used for internal fertilization.

Cynopoecilus is derived from two generic names: Regan combined Cynolebias (egg layers) and Poecilia (live-bearers). Cynopoecilus spp. can stand temperatures as low as 12C, and as high as 30C.

Cynopoecilus share their biotype with other Rivulid genera including Rivulus and Austrolebias, and are replaced by Campellolebias to the north.

Behavior:

In the natural habitat, winter can be cold. Also, waters can evaporate during dry periods. However, they also live in swamps and pools that have water for the entire year. It has alsobeen reported that reproduction can take place without a dry incubation period.
As males can be territorial and very aggressive to each other, this species is not for inexperienced hobbyists. The nickname of the type species is “Fighting Gaucho”, and this is not without reason. To breed these fishes a small tank will do, if more than one female is put to the male. While fighting, the males become deeply colored, showing beautiful patterns and colors, and display their fins in wild movements.