The mangrove rivulus or mangrove killifish, ''Kryptolebias marmoratus'' ( syn. ''Rivulus marmoratus''), is a species of

killifish A killifish is any of various oviparous (egg-laying) cyprinodontiform fish, including families Aplocheilidae, Pantanodontidae, Cyprinodontidae, Fundulidae, Nothobranchiidae, Profundulidae, Aphaniidae and Valenciidae. All together, there ar ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Rivulidae The Rivulidae are a family (biology), family of killifishes in the order (biology), order Cyprinodontiformes. They are commonly known as rivulids, South American killifish or New World killifish. The latter names are slightly misleading, however, ...

. It lives in

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

and marine waters (less frequently in fresh water) along the coasts of

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, through the

Antilles The Antilles is an archipelago bordered by the Caribbean Sea to the south and west, the Gulf of Mexico to the northwest, and the Atlantic Ocean to the north and east. The Antillean islands are divided into two smaller groupings: the Greater An ...

, and along the eastern and northern Atlantic coasts of Mexico, Central America and South America (south to Brazil). It has a very wide tolerance of both

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

(0–68

‰ The phrase per mille () indicates parts per thousand. The associated symbol is , similar to a per cent sign but with an extra zero in the divisor. Major dictionaries do not agree on the spelling, giving other options of per mil, per mill, pe ...

)Bester, C
Mangrove Rivulus.
Florida Museum. Retrieved 6 May 2017. and temperature (),Hill, K

Smithsonian Marine Station at Fort Pierce. Retrieved 6 May 2017. can survive for about two months on land, and mostly breeds by

self-fertilization Autogamy or self-fertilization refers to the Cell fusion, fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a Reproduction, reproductive mechanism employed by many flowering pl ...

. It is typically found in areas with

red mangrove Red mangrove may refer to at least three plant species: * ''Rhizophora mangle'' * ''Rhizophora mucronata ''Rhizophora mucronata'' (loop-root mangrove, red mangrove or Asiatic mangrove) is a species of mangrove found on coasts and river banks in E ...

and sometimes lives in burrows of ''

Cardisoma guanhumi ''Cardisoma guanhumi'', also known as the blue land crab or great land crab, is a species of land crab found in tropical and subtropical estuaries and other maritime areas of land along the Atlantic Ocean, Atlantic coast of the Americas from Bra ...

'' crabs. The mangrove rivulus is up to long, but most individuals are . Overall the mangrove rivulus is widespread and not threatened, but in the United States it is considered a Species of Concern by the

National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the ste ...

.National Marine Fisheries Service (23 February 2017)
Species of Concern List
Retrieved 6 May 2017.

Ecology

Land living

The mangrove rivulus can spend up to 66 consecutive days out of water, which it typically spends inside fallen logs, breathing air through its skin."Tropical fish can live for months out of water"
Reuters, Wed Nov 14, 2007 9:05pm GMT It enters burrows created by insects inside trees where it relaxes its territorial, aggressive behavior. During this time, it alters its

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s so it can retain water and nutrients, while

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

waste is excreted through the skin. The change is reversed once it re-enters the water. When jumping on land, the mangrove rivulus 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 The Society for Experimental Biology is a learned society for animal, cell and plant biologists. It was founded in 1923 at Birkbeck College to "promote the art and science of experimental biology in all its branches". It aims to demonstrate the im ...

released a video in 2013 showing the jumping technique.

Breeding

Spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

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

, but males do exist, and strong genetic evidence indicates occasional

outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing in animals Out ...

. 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 Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mos ...

clones, but in highly colonized South and Central American pools males typically are 3 to 8% of the population, and in offshore cays in

Belize Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...

20 to 25% are males. ''K. marmoratus'' produces eggs and sperm by

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

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 self-fertilization 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 Inbreeding depression is the reduced biological fitness caused by loss of genetic diversity as a consequence of inbreeding, the breeding of individuals closely related genetically. This loss of genetic diversity results from small population siz ...

. 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 cell A germ cell is any cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads. There, they unde ...

s 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 Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertiliz ...

. Adults may cannibalize juveniles, but only unrelated offspring.

Epigenetic studies

Because ''K. marmoratus'' can reproduce consistently by self-fertilization, it gives rise to isogenic lineages. These lineages afford the opportunity to explicitly investigate

epigenetic In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...

phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

effects in genetically identical individuals. Epigenetic changes due to

DNA methylation DNA methylation is a biological process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter (genetics), promoter, DNA methylati ...

were studied, and specific patterns of DNA methylation at

CpG site The CpG sites or CG sites are regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5' → 3' direction. CpG sites occur with high frequency in genomic regions called CpG isl ...

s in adults and during development were found to occur.

Conservation

Overall the mangrove rivulus is widespread and not threatened, but in the United States it is considered a Species of Concern by the

. It is considered a species of

Least Concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...

by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

, and was formerly listed as a species of special concern in Florida, but has since been delisted. It was formerly often overlooked and considered rare in Florida, but surveys have revealed that it is locally common in this state and abundant in the

Florida Keys The Florida Keys are a coral island, coral cay archipelago off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami a ...

. It is considered vulnerable by the American Fisheries Society. The mangrove rivulus is considered to have potential as a

bioindicator A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other sma ...

species of

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...

habitats.

References

External links

{{Authority control Rivulidae Fish of the Atlantic Ocean Fish of North America Fish of South America Amphibious fish Fish described in 1880 Taxa named by Felipe Poey Taxonomy articles created by Polbot