The male is not required for breeding. They require brackish water – one leveled teaspoon of marine salt per every 2 liters of water. This species grows up to approx 50 mm in size.
The Mangrove Killifish or Mangrove Rivulus, Kryptolebias marmoratus, is a species of fish in the Aplocheilidae family. It lives in brackish and marine waters (less frequently in fresh water) along the coasts of Florida, through the Antilles, and along the eastern and northern Atlantic coasts of Mexico, Central America and South America. Our fish originates from Belize. It has a very wide tolerance of both salinity (0—68 ‰) and temperature (12–38 °C or 54–100 °F), can survive for about two months on land, and mostly breeds by self-fertilization. It is typically found in areas with red mangrove and sometimes lives in burrows of Cardisoma guanhumi crabs.
Kryptolebias marmoratus can spend up to 66 consecutive days out of water, which it typically spends inside fallen logs, breathing air through its skin. It enters burrows created by insects inside trees where it relaxes its territorial, aggressive behaviour. During this time, it alters its gills so it can retain water and nutrients, while nitrogen waste is excreted through the skin. The change is reversed once it re-enters the water.
When jumping on land, Kryptolebias marmoratus does a “tail flip”, flipping its head over its body towards the tail end. The rivulus’ jumping technique gives it an ability to direct its jumps on land and to make relatively forceful jumps. A team of scientists associated with the Society for Experimental Biology released a video in 2013 showing the jumping technique.
The species consists mostly of hermaphrodites which are known to reproduce by self-fertilization, but males do exist, and strong genetic evidence indicates occasional outcrossing. They are also the only simultaneous hermaphroditic vertebrates, and the concentration of males to hermaphrodites can vary depending on the local requirement for genetic diversity.
Kryptolebias marmoratus produces eggs and sperm by meiosis and routinely reproduces by self-fertilization. Each individual hermaphrodite normally fertilizes itself when an egg and sperm that it has produced by an internal organ unite inside the fish’s body. In nature, this mode of reproduction can yield highly homozygous lines composed of individuals so genetically uniform as to be, in effect, identical to one another. The capacity for selfing in these fishes has apparently persisted for at least several hundred thousand years. Meioses that lead to self-fertilization can reduce genetic fitness by causing inbreeding depression. However, self-fertilization does provide the benefit of “fertilization assurance” (reproductive assurance) at each generation. Meiosis can also provide the adaptive benefit of efficient recombinational repair of DNA damages during formation of germ cells at each generation. This benefit may have prevented the evolutionary replacement of meiosis and selfing by a simpler type of clonal reproduction such as ameiotic or apomictic parthenogenesis. Cannibalization of fingerling occurs, but only unrelated offspring. Kryptolebias marmoratus is considered to have potential as a bioindicator species of estuary habitats.