Arapaimidae

{{Short description|Subfamily of ray-finned fishes}} {{Automatic taxobox | image = Arapaima gigas1.jpg | image_caption = ''Arapaima'' sp. | taxon = Arapaimidae | authority = Bonaparte, 1846 | subdivision_ranks = Genera | subdivision_ref = <ref name="FishBase">{{FishBase family | family = Osteoglossidae| month = July | year = 2021}}</ref> | subdivision = * ''Arapaima'' * ''Heterotis'' | synonyms = Sudidinae }}

'''Arapaimidae''' is a family of freshwater ray-finned fish belonging to the order Osteoglossiformes. It includes the South American arapaimas of the Amazon and Essequibo basins and the African arowana (''Heterotis niloticus'') from the watersheds of the Sahelo-Sudanese region, Senegal, Gambia, and parts of Eastern Africa.<ref name="FishBase" /> This family is sometimes treated as the subfamily '''Arapaiminae'''.<ref name=":1" /><ref name=":0">{{Cite book|last1=Hastings|first1=P. A.|title=Fishes: a guide to their diversity|last2=Walker, Jr.|first2=H. J.|last3=Galland|first3=G. R.|publisher=University of California Press|year=2014|isbn=978-0-520-28353-4|location=Oakland, California|pages=62–64}}</ref> A commonly used synonym is '''Heterotidinae''',<ref name="Nelson2016">{{cite book|last1=Nelson|first1=Joseph S.|last2=Grande|first2=Terry C.|last3=Wilson|first3=Mark V. H.|year=2016|title=''Fishes of the World''|edition=5th|url=https://sites.google.com/site/fotw5th/|publisher=John Wiley & Sons|isbn=978-1-118-34233-6|access-date=2021-07-16|archive-date=2019-04-08|archive-url=https://web.archive.org/web/20190408194051/https://sites.google.com/site/fotw5th/}}</ref> but according to the ICZN, Arapaimidae has priority.<ref name=":1" />

Arapaimides, along with other osteoglossomorphs, are of phylogenetic and evolutionary interest due to their trans-oceanic distribution, excellent fossil record, and position as one of the oldest living teleost lineages.<ref name=":0" /> The type-species of the group, ''Arapaima gigas'', is an important South American food source and charismatic representative of the region.<ref name=":3">{{Cite journal|last=Stewart|first=J. D.|date=2013a|title=Re-description of Arapaima agassizii (Valenciennes), a rare fish from Brazil (Osteoglossimorpha: Osteoglossidae)|journal=Copeia|volume=2013|issue=1|pages=38–51|doi=10.1643/CI-12-013|s2cid=84207464}}</ref> Both ''Arapaima'' and ''Heterotis'' are cultured for food in their respective countries due to their heartiness and meat, and the arapaima is a prized sport-fish, being the largest truly freshwater fish.<ref name=":2">{{Cite journal|last1=Vitorino|first1=R. C.|last2=Oliverira|first2=C.|last3=Margarido|first3=V. P.|last4=Venere|first4=P. C.|date=2015|title=Genetic diversity of Arapaima gigas (Schinz, 1822) (Osteoglossimorpha: Arapaimidae) in the Araguaia-Tocantins basin estimated by ISSR marker|journal=Neotropical Ichthyology|volume=13|issue=3|pages=557–568|doi=10.1590/1982-0224-20150037|doi-access=free}}</ref>

== Phylogeny and systematics == The internal placement of Osteoglossomorpha within crown-group teleosts is contested, with competing morphological and molecular analyses placing them either as sister to all other extant teleosts, or internal to Elopimorpha and sister to the clade consisting of Otocephala and Euteleostei.<ref name=":1">{{Cite journal|last1=Hilton|first1=E. J.|last2=Lavoue|first2=Sebastien|date=2018|title=A review of the systematic biology of fossil and living bony-tongue fishes, Osteoglossimorpha (Actinopterygii: Teleostei)|journal=Neotropical Ichthyology|volume=16|issue=3|article-number=e180031|doi=10.1590/1982-0224-20180031|s2cid=92396368|doi-access=free}}</ref><ref name=":7">{{Cite journal|last1=Lavoue|first1=Sullivan|last2=Sullivan|first2=J. P.|date=2004|title=Simultaneous analysis of five colecular markers provides a well-supported phylogenetic hypothesis for the living bony-tongue fishes (Osteoglossimorpha: Teleostei)|journal=Molecular Phylogenetics and Evolution|volume=33|issue=2014|pages=171–185|doi=10.1016/j.ympev.2004.04.021|pmid=15324846|bibcode=2004MolPE..33..171L }}</ref> alt=Phylogram showing the internal relationships of the clades that make up the order Osteoglosiformes, including: Mormyridae, Gymnarchidae, Notopteridae, Heterotis, Arapaima, Scleropages, Osteoglossum, and Panteodontidae|center|thumb|779x779px

The placement and name of the clade containing ''Arapaima'' and ''Heterotis'' is also uncertain. Some include this clade in the family Osteoglossidae with the South American and Asian arowana.<ref name=":2" /> Others place ''Arapaima'' and ''Heterotis'' together in their own family, Arapaimidae. alt=Phylograms showing the hypothesis of the relationships of internal Osteoglossimorphs: Heterotis, Arapaima, Scleropages, and Osteoglossum (based on Hastings, Walker, and Galland 2014)|center|thumb|706x706px

==Taxonomy== ''Arapaima'' taxonomy was recently revised to revalidate old names and describe a new species, proposing 6 existing species (see below) and invalidating current museum specimens.<ref name=":3" /><ref name=":4">{{Cite journal|last1=Farias|first1=Izeni Pires|last2=Willis|first2=Stuart|last3=Leão|first3=Adam|last4=Verba|first4=Júlia Tovar|last5=Crossa|first5=Marcelo|last6=Foresti|first6=Fausto|last7=Porto-Foresti|first7=Fabio|last8=Sampaio|first8=Iracilda|last9=Hrbek|first9=Tomas|date=2019-08-16|title=The largest fish in the world's biggest river: Genetic connectivity and conservation of Arapaima gigas in the Amazon and Araguaia-Tocantins drainages|journal=PLOS ONE|language=en|volume=14|issue=8|article-number=e0220882|doi=10.1371/journal.pone.0220882|issn=1932-6203|pmc=6697350|pmid=31419237|bibcode=2019PLoSO..1420882F|doi-access=free}}</ref><ref name=":5">{{Cite journal|last=Stewart|first=Donald J.|date=2013-09-27|title=A New Species of Arapaima (Osteoglossomorpha: Osteoglossidae) from the Solimões River, Amazonas State, Brazil|url=http://www.bioone.org/doi/abs/10.1643/CI-12-017|journal=Copeia|language=en|volume=2013|issue=3|pages=470–476|doi=10.1643/CI-12-017|s2cid=85752227|issn=0045-8511|url-access=subscription}}</ref> However, these four proposed or reestablished species are known only from singular holotype specimens, and only that of ''A. mapae'' and ''A. leptostoma'' still currently exist.<ref name=":3" /><ref name=":4" /><ref name=":5" /> Typically, all species of ''Arapaima'' described by Valenciennes, Spix, and Agassiz are referred to as ''A. gigas'', though current taxonomy could be revised with more thorough evidence.<ref name=":4" /> Currently, population genetic evidence supports a singular ''Arapaima'' species with two distinct genetic populations: an Amazonas population (exhibiting a pattern of isolation by distance), and an Araguaia-Tocantins basin population.<ref name=":4" /> There is little debate that ''Heterotis'' is a monotypic genus represented by only ''H. niloticus''.

* '''Arapaimidae''' Bonaparte, 1846<ref name="FishBase" /><ref name=":1" /> ** {{Extinct}}''Arapaimidarum'' [otolith] ** {{Extinct}}''Heterotidinarum'' Nolf, Rana & Prasad 2008 [otolith] ** {{Extinct}}''Thrissopterus'' Heckel 1856 ** {{Extinct}}''Joffrichthys''? Li & Wilson 1996 ** {{Extinct}}''Sinoglossus''? Su 1986 ** ''Heterotis'' Rüppell 1829 ex Ehrenberg 1836 (African arowana) *** ''H. niloticus'' (Cuvier, 1829) ** ''Arapaima'' Müller 1843 (arapaima) *** ''A. agassizii'' (Valenciennes, 1847) *** ''A. gigas'' (Schinz, 1822) *** ''A. leptosoma'' Stewart, 2013 *** ''A. mapae'' (Valenciennes, 1847) *** ''A. sp.'' ''incertae sedis''

== Description and biology ==

=== Description === thumb|367x367px|Illustration by Louis Agassiz of what is now considered the type specimen for ''A. agassizii'', with osteological study (from Spix and Agassiz, 1829) Arapaimides are characterized by elongate, slender bodies with large scales and long dorsal and anal fins positioned close to a short caudal peduncle.<ref name="FishBase" /><ref name=":0" /> The pelvic fins are small and abdominal if present.<ref name="FishBase" /><ref name=":0" /> They lack chin barbels, have a glossolaryngeal (tongue) bone with teeth present, and the premaxillae are fixed to the skull.<ref name="FishBase" /><ref name=":0" /> Branched caudal fin rays are less than sixteen, branchiostegal rays between three and seven, and hypurals less than 6.<ref name="FishBase" /><ref name=":0" /> ''Heterotis'' possesses a specialized suprabranchial organ for concentrating and filtering small food particles.<ref name="FishBase" /><ref name=":7" />

=== Biology === Both genera make use of similar freshwater habitats in the respective region, with ''Arapaima'' found in the floodplains of the Amazon and Esequibo river basins of South America and ''Heterotis'' found in littoral zones of large, open rivers in all Sahelo-Sudanese basins of Africa.<ref name=":8">{{Cite web|title=Heterotis niloticus, African bonytongue: fisheries, aquaculture, aquarium|url=https://www.fishbase.se/summary/Heterotis-niloticus|access-date=2021-04-24|website=www.fishbase.se}}</ref><ref name=":9">{{Cite web|title=Arapaima gigas, Arapaima: fisheries, aquaculture, gamefish, aquarium|url=https://www.fishbase.se/summary/Arapaima-gigas.html|access-date=2021-04-24|website=www.fishbase.se}}</ref> ''Arapaima'' is typically a top-water fish predator, while ''Heterotis'' is a benthic mud-filterer primarily feeding on phytoplankton and small crustaceans with their suprabranchial organ.<ref name=":8" /><ref name=":9" /> Both groups are obligate air-breathers and nest-builders, with males guarding eggs and young.<ref name=":8" /><ref name=":9" />

== Evolution == A genetic study shows that Arapaimidae diverged from Osteoglossinae about 220 million years ago, during the Late Triassic. Within Osteoglossinae, the lineage leading to the South American ''Osteoglossum'' arowanas diverged about 170 million years ago, during the Middle Jurassic. The Asian and Australian arowanas in the genus ''Scleropages'' separated about 140 million years ago, during the Early Cretaceous.<ref name=":10">{{Cite journal|date=2016-06-01|title=Was Gondwanan breakup the cause of the intercontinental distribution of Osteoglossiformes? A time-calibrated phylogenetic test combining molecular, morphological, and paleontological evidence|url=https://www.sciencedirect.com/science/article/abs/pii/S1055790316000841|journal=Molecular Phylogenetics and Evolution|language=en|volume=99|pages=34–43|doi=10.1016/j.ympev.2016.03.008|issn=1055-7903|last1=Lavoué|first1=Sébastien|pmid=26979263|bibcode=2016MolPE..99...34L |url-access=subscription}}</ref><ref name=":11">{{Cite journal|last1=Lundberg|first1=John G.|last2=Chernoff|first2=Barry|date=1992|title=A Miocene Fossil of the Amazonian Fish Arapaima (Teleostei, Arapaimidae) from the Magdalena River Region of Colombia--Biogeographic and Evolutionary Implications|journal=Biotropica|volume=24|issue=1|pages=2–14|doi=10.2307/2388468|jstor=2388468|bibcode=1992Biotr..24....2L |issn=0006-3606}}</ref>

Originally, it was thought that the breakup of Gondwana 150 – 30 million years ago was the evolutionary cause of the trans-continental distribution of the osteoglossomorphs. However, minimum ages of intercontinental clades and presence of marine forms in the fossil records imply that ancestral trans-oceanic dispersal is possible. Tests of these hypotheses are currently inconclusive as they are dependent on an ''a priori'' calibrated age of crown-group Teleostei, about which fossil and molecular evidence disagree. I.e., hypotheses do not fail only if Teleostei are of Permian origin, but molecular inferences push crown ages further back.<ref name=":0" /><ref name=":10" /><ref name=":11" /><ref name=":5" /> [[File:Paiche en Belen.jpg|thumb|189x189px|Salted paiche (''Arapaima gigas'') stall in Mercado de Bele, Iquitos, Peru]]

== Use by humans == Both ''Arapaima'' and ''Heterotis'' are farmed in their respective regions as relatively large and hardy food-fish.<ref name="FishBase" />

== Etymology == The family is named after the monotypic genus ''Arapaima'', whose name derives from the Tupi-Guyarana indigenous name for ''Arapaima gigas''. <gallery> File:Arapaima gigas in aqua park.jpg|''A. gigas'' in aquarium File:Arapaima gigas at Beijing aquarium.JPG|''A. gigas'' in aquarium File:Heterotis niloticus.png|''H. niloticus'' in aquarium File:Heterotis niloticus MHNT ICHT 1995 69.jpg|Museum specimen of ''H. niloticus'' </gallery>

==References== {{Reflist}}

Category:Osteoglossidae Category:Actinopterygii subfamilies