Wilson J. E. Costa split this genus into several new genera (including Anablepsoides, Atlantirivulus, Cynodonichthys, Kryptolebias, Laimosemion and Melanorivulus) in 2004 and 2011, leaving only a few Greater Antillean species in Rivulus itself.

Huber refuted the split, moving the proposed genera back in Rivulus and again making the genus the largest in the family Aplocheilidae.

[3][4][5] If the split into multiple genera is not recognized, Rivulus contains more than 150 non-annual killifish species found in fresh and brackish waters of the tropical and subtropical Americas, ranging from Argentina in south to Mexico in north, including the Caribbean region.

[3][6] The two Cuban species are close relatives,[4] but the position of the Hispaniolan R. roloffi has not been confirmed and its placement in this genus is preliminary.

[1][5] Because of the disputed validity of the split into several genera, there is a level of confusion about the species included in Rivulus, despite it being clearly defined in 2011.