Kryptolebias was described by W. Costa (2004) on the basis of osteological differences (of four species previously assigned to Rivulus). In his paper he used the name Cryptolebias, but it was preoccupied by a Miocene fossil fish (from present-day Italy). Thus, Costa (2004a) was compelled to make an amendment, which became Kryptolebias. Vermeulen & Hrbek (2005) subsequently supported the generic status of Kryptolebias with mitochondrial DNA sequence evidence, describing a fifth member K. sepia.
Kryptolebias is an older genus than Rivulus. A plausible hypothesis is that Rivulus evolved from coastal/estuarine species, and adapted to fresh waters and inland habitats.
Three of the four species in Costa's description had their habitat in south-east Brazil, not too far from the coastline. The fourth species is a marine hermaphrodite species living along the coast from Florida, the Caribbean Islands (including the easterly coastline of South America) down to the Brazil. The species described by Vermeulen & Hrbek, however, lives far from the other members, in Surinam. It is believed by the senior author that new expeditions in the huge area between the two localities will discover more species belonging to this genus.
Kryptolebias brasiliensis - male. © Image made by F.Vermeulen.
Although four of the five members live in fresh water, it is clear that brackish water boosts their reproduction and well-being. Also, the marine hermaphrodite species K. marmoratus (which normally lives in crab holes in mangrove areas) can be kept in brackish-, or even pure-, freshwater, if the change is not too sudden.
In general, members of this genus behave similarly to Rivulus spp. Thus they can jump out of the water, to seek new pools, to find a niche for shelter and food. They feed mainly on flying insects, ants and mosquito larvae. But crustaceans and tadpoles are among their favored food.
For more details concerning behavior, how to keep and how to breed, click the link that leads to each species.