Spawning has not yet been observed in the wild in the mangrove rivulus, but captive studies show that the eggs are positioned in shallow water, sometimes even in places that periodically are on land during low tide.
The eggs can continue their development when out of water, but once they are ready to hatch this is delayed until again submerged.

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 (for example, if an increase in the local parasite population occurred, secondary male numbers might increase).
In Florida, almost all (>99%) are homozygous clones, but in highly colonized South and Central American pools males typically are 3—8% of the population, and in offshore cays in Belize 20—25% are males.

K. 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.
Adults may cannibalize juveniles, but only unrelated offspring.
Spawning has not yet been observed in the wild in the mangrove rivulus, but captive studies show that the eggs are positioned in shallow water, sometimes even in places that periodically are on land during low tide. The eggs can continue their development when out of water, but once they are ready to hatch this is delayed until again submerged.
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 (for example, if an increase in the local parasite population occurred, secondary male numbers might increase). In Florida, almost all (>99%) are homozygous clones, but in highly colonized South and Central American pools males typically are 3—8% of the population, and in offshore cays in Belize 20—25% are males.
K. 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. Adults may cannibalize juveniles, but only unrelated offspring.
Mangrove rivulus