''Rivulus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of small freshwater

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

in the

Cyprinodontiformes Cyprinodontiformes is an order (biology), order of Actinopterygii, ray-finned fish, comprising mostly small, freshwater fish. Many popular aquarium fish, such as killifish and Poeciliidae, live-bearers, are included. They are closely related t ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Rivulidae The Rivulidae are a family of killifishes in the order Cyprinodontiformes. They are commonly known as rivulids, South American killifish or New World killifish. The latter names are slightly misleading, however, as they are neither restricted to ...

. It was traditionally considered to be the largest genus in its family; however, the genus's size is currently in dispute. Wilson J. E. Costa split this genus into several new genera (including ''

Anablepsoides ''Anablepsoides'' is a genus of killifish in the family Rivulidae native to tropical South America and the Lesser Antilles. The majority are from the Amazon and Orinoco basins, as well as freshwater systems in the Guiana Shield, but a few species ...

Atlantirivulus ''Atlantirivulus'' is a genus of fishes in the family Rivulidae. They are endemic to shallow swamps, creeks, streams and pools in the Atlantic Forest in southeastern Brazil, ranging from Rio de Janeiro to Santa Catarina.Costa, W.J.E.M. (2014)Fou ...

Cynodonichthys ''Cynodonichthys'' is a genus of freshwater killifish in the family Rivulidae. They are found in Middle America, ranging from southern Mexico (north to Oaxaca and the Yucatán Peninsula), through Central America (where most species live), to Col ...

'', '' Kryptolebias'', ''

Laimosemion ''Laimosemion'' is a genus of fish in the family Rivulidae from the Amazon basin and basins in the Guiana Shield in tropical South America. They mostly inhabit small streams, creeks, swamps and pools in lowlands, but locally occur to an altitude ...

'' and ''

Melanorivulus ''Melanorivulus'' is a genus of South American freshwater fish in the family Rivulidae. Most species are endemic to the Río de la Plata, eastern Amazon (west to Tapajós basin), Tocantins– Araguaia and São Francisco basins in Brazil, but a f ...

'') in 2004 and 2011, leaving only a few Greater Antillean species in ''Rivulus'' itself. Despite being moved to other genera, some of the species retain the common name "rivulus", like the well-known

mangrove rivulus The mangrove killifish or mangrove rivulus, ''Kryptolebias marmoratus'' ( syn. ''Rivulus marmoratus''), is a species of killifish in the family Rivulidae. It lives in brackish and marine waters (less frequently in fresh water) along the coasts ...

(''Kryptolebias marmoratus''). Shortly after the review by Costa, another review authored by J.H. Huber refuted the split, moving the proposed genera back in ''Rivulus'' and again making the genus the largest in the family Aplocheilidae.Huber, J.H., 2012. Reappraisal of the Phylogeny of Rivulus and its Allied Focused on External Characters. Killi-Data Series 2012: 9-25. If the split is recognized, the genus ''Rivulus'' only includes three non-annual

killifish A killifish is any of various oviparous (egg-laying) cyprinodontiform fish (including families Aplocheilidae, Cyprinodontidae, Fundulidae, Profundulidae and Valenciidae). All together, there are 1,270 species of killifish, the biggest family ...

species from western

Cuba Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...

(including

Isla de la Juventud Isla de la Juventud (; en, Isle of Youth) is the second-largest Cuban island (after Cuba's mainland) and the seventh-largest island in the West Indies (after mainland Cuba itself, Hispaniola, Jamaica, Puerto Rico, Trinidad, and Andros Islan ...

) and

Hispaniola Hispaniola (, also ; es, La Española; Latin and french: Hispaniola; ht, Ispayola; tnq, Ayiti or Quisqueya) is an island in the Caribbean that is part of the Greater Antilles. Hispaniola is the most populous island in the West Indies, and th ...

where they inhabit streams, rivers and lagoons from the highlands to the coast. If the split into multiple genera is not recognized, ''Rivulus'' contains more than 150 non-annual killifish species found in fresh and

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 ...

waters of the tropical and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...

Americas, ranging from Argentina in south to Mexico in north, including the Caribbean region.

Species

Three species are included in ''Rivulus'': * ''

Rivulus berovidesi ''Rivulus'' is a genus of small freshwater fish in the Cyprinodontiformes family Rivulidae. It was traditionally considered to be the largest genus in its family; however, the genus's size is currently in dispute. Wilson J. E. Costa split this ge ...

'' R. R. Silva, 2015 * ''

Rivulus cylindraceus ''Rivulus'' is a genus of small freshwater fish in the Cyprinodontiformes family Rivulidae. It was traditionally considered to be the largest genus in its family; however, the genus's size is currently in dispute. Wilson J. E. Costa split this ge ...

'' Poey, 1860 (Green rivulus) * ''

Rivulus roloffi ''Rivulus'' is a genus of small freshwater fish in the Cyprinodontiformes family Rivulidae. It was traditionally considered to be the largest genus in its family; however, the genus's size is currently in dispute. Wilson J. E. Costa split this ge ...

'' Roloff, 1938 (Hispaniolan rivulus)Lyons, T.J. & Torres-Pineda, P. 2021. Rivulus roloffi. The IUCN Red List of Threatened Species 2021: e.T125990534A125990585. https://dx.doi.org/10.2305/IUCN.UK.2021-1.RLTS.T125990534A125990585.en. Downloaded on 06 September 2021. A fourth species, ''R. insulaepinorum'', has been recognized, but it is a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of ''R. cylindraceus''. The two Cuban species are close relatives, but the position of the Hispaniolan ''R. roloffi'' has not been confirmed and its placement in this genus is preliminary. 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. For example, ''"R." azureus'', ''"R." pivijay'', ''"R." ribesrubrum'', ''"R." tomasi'' and ''"R." xi'' were described in 2013 by authors that did not recognize the split of ''Rivulus'', but noted that they were part of ''

'' (most species) and ''

'' (''"R." tomasi''), by them only considered subgenera of ''Rivulus''. This has resulted in the unusual situation where

FishBase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

, despite recognizing the split into several genera, places the newly described species that belong in other genera in ''Rivulus''.

References

{{Taxonbar, from=Q798213 Rivulidae Freshwater fish genera Taxa named by Felipe Poey Fish of the Dominican Republic