Rivulus

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 genus into several new genera (including Anablepsoides, Atlantirivulus, Cynodonichthys, Kryptolebias, Laimosemion and Melanorivulus) in 2004 and 2011, leaving only a few Greater Antillean species in Rivulus itself.[1] Despite being moved to other genera, some of the species retain the common name "rivulus", like the well-known mangrove rivulus (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.[2]

Rivulus
Rivulus cylindraceus (male)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Rivulidae
Genus: Rivulus
Poey, 1860
Type species
Rivulus cylindraceus
Poey, 1860

If the split is recognized, the genus Rivulus only includes three non-annual killifish species from western Cuba (including Isla de la Juventud) and Hispaniola where they inhabit streams, rivers and lagoons from the highlands to the coast.[3][4][5] If the split into multiple genera is not recognized, Rivulus contains more than 150 non-annual killifish species found in fresh and brackish waters of the tropical and subtropical Americas, ranging from Argentina in south to Mexico in north, including the Caribbean region.[2]

Species

Three species are included in Rivulus:[1][3][4]

  • Rivulus berovidesi R. R. Silva, 2015
  • Rivulus cylindraceus Poey, 1860 (Green rivulus)
  • Rivulus roloffi Roloff, 1938 (Hispaniolan rivulus)

A fourth species, R. insulaepinorum, has been recognized, but it is a synonym of R. cylindraceus.[3][6] The two Cuban species are close relatives,[4] but the position of the Hispaniolan R. roloffi has not been confirmed and its placement in this genus is preliminary.[1][5]

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.[1] 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 Cynodonichthys (most species) and Laimosemion ("R." tomasi), by them only considered subgenera of Rivulus.[7][8] This has resulted in the unusual situation where FishBase, despite recognizing the split into several genera, places the newly described species that belong in other genera in Rivulus.[9] This is repeated by Catalog of Fishes, which also recognizes the split into several genera, but includes the newly described "R." azureus, "R." pivijay, "R." ribesrubrum and "R." xi,[6] despite them being part of Cynodonichthys according to their description.[8]

References
  1. Costa W.J.E.M. (2011). "Phylogenetic position and taxonomic status of Anablepsoides, Atlantirivulus, Cynodonichthys, Laimosemion and Melanorivulus (Cyprinodontiformes: Rivulidae)". Ichthyological Exploration of Freshwaters. 22 (3): 233–249.
  2. Huber, J.H., 2012. Reappraisal of the Phylogeny of Rivulus and its Allied Focused on External Characters. Killi-Data Series 2012: 9-25.
  3. Ponce De León, José Luis; León, Gunnary; Rodríguez, Rodet; Metcalfe, Cushla J.; Hernández, Damir; Casane, Didier; García-Machado, Erik (2014). "Phylogeography of Cuban Rivulus: Evidence for allopatric speciation and secondary dispersal across a marine barrier". Molecular Phylogenetics and Evolution. 79: 404–414. doi:10.1016/j.ympev.2014.07.007. PMID 25050928.
  4. Silva, Rodet Rodriguez (2015). "Rivulus berovidesi, a new killifish species (Teleostei: Rivulidae) from western Cuba". Zootaxa. 3949 (2): 289–96. doi:10.11646/zootaxa.3949.2.9. PMID 25947808.
  5. Loureiro, M.; R. de Sá; S.W. Serra; F. Alonso; L.S.K. Lanés; M.V. Volcan; P. Calviño; D. Nielsen; A. Duarte; G. Garcia (2018). "Review of the family Rivulidae (Cyprinodontiformes, Aplocheiloidei) and a molecular and morphological phylogeny of the annual fish genus Austrolebias Costa 1998". Neotrop. Ichthyol. 16 (3). doi:10.1590/1982-0224-20180007.
  6. Eschmeyer, William N.; Fricke, Ron & van der Laan, Richard (eds.). "Species in the genus Rivulus". Catalog of Fishes. California Academy of Sciences. Retrieved 21 March 2019.
  7. Vermeulen, F.B.M.; Valdesalici, S.; Garcia-Gil, J.R. (2013). "Rivulus tomasi (Teleostei: Cyprinodontiformes: Rivulidae), a new killifish from Tobogán de la Selva, middle Orinoco river drainage in the Amazonas Territory, southwest Venezuela". Aqua, International Journal of Ichthyology. 19 (4): 187–192.
  8. Vermeulen, F.B.M. (2013). "Four new species of Rivulus Poey, 1860, subgenus Cynodonichthys Meek, 1904 (Teleostei: Cyprinidontiformes: Rivulidae) from the Magdalena River Basin, Central Colombia, including notes on Rivulus (Cynodonichthys) elegans Steindachner, 1880". Killi-data Series. 2013: 42–63.
  9. Froese, Rainer and Pauly, Daniel, eds. (2019). Species of Rivulus in FishBase. March 2019 version.
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