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Arapaiminae is a subfamily of freshwater osteoglossiform (bony-tongued) fishes belonging to the family
Osteoglossidae Osteoglossidae is a family of large freshwater fish, which includes the arowanas and arapaima. The family contains two subfamilies Arapaiminae and Osteoglossinae, with a total of five living genera. Osteoglossids are basal teleosts that origin ...
. It includes the South American
arapaima The arapaima, pirarucu, or paiche is any large species of bonytongue in the genus ''Arapaima'' native to the Amazon and Essequibo basins of South America. ''Arapaima'' is the type genus of the subfamily Arapaiminae within the family Osteoglo ...
s of the
Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...
and Essequibo basins and the African arowana (''Heterotis niloticus'') from the watersheds of the Sahelo-Sudanese region,
Senegal Senegal,; Wolof: ''Senegaal''; Pulaar: 𞤅𞤫𞤲𞤫𞤺𞤢𞥄𞤤𞤭 (Senegaali); Arabic: السنغال ''As-Sinighal'') officially the Republic of Senegal,; Wolof: ''Réewum Senegaal''; Pulaar : 𞤈𞤫𞤲𞤣𞤢𞥄𞤲𞤣� ...
,
Gambia The Gambia,, ff, Gammbi, ar, غامبيا officially the Republic of The Gambia, is a country in West Africa. It is the smallest country within mainland AfricaHoare, Ben. (2002) ''The Kingfisher A-Z Encyclopedia'', Kingfisher Publicatio ...
, and parts of Eastern Africa. This subfamily is sometimes raised to the rank of family, as Arapaimidae. A commonly used synonym is Heterotidinae, but according to the
ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...
, Arapaiminae has priority. Arapaimines, along with other
osteoglossomorph Osteoglossomorpha is a group of bony fish in the Teleostei. Notable members A notable member is the arapaima (''Arapaima gigas''), the largest freshwater fish in South America and one of the largest bony fishes alive. Other notable members incl ...
s, are of
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
and evolutionary interest due to their trans-oceanic distribution, excellent fossil record, and position as one of the oldest living
teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
lineages. The type-species of the group, ''
Arapaima gigas ''Arapaima gigas'', also known as pirarucu, is a species of arapaima native to the basin of the Amazon River. Once believed to be the sole species in the genus, it is among the largest freshwater fish. The species is an obligate air-breather, s ...
'', is an important South American food source and charismatic representative of the region. 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.


Phylogeny and systematics

The internal placement of Osteoglossomorpha within crown-group teleosts is contested, with competing morphological and
molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
analyses placing them either as sister to all other
extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extin ...
teleosts, or internal to Elopimorpha and sister to the clade consisting of Otocephala and Euteleostei. 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. Others place ''Arapaima'' and ''Heterotis'' together in their own family, Arapaimidae.


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. However, these four proposed or reestablished species are known only from singular
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
specimens, and only that of ''A. mapae'' and ''A. leptostoma'' still currently exist. Typically, all species of ''Arapaima'' described by
Valenciennes Valenciennes (, also , , ; nl, label=also Dutch, Valencijn; pcd, Valincyinnes or ; la, Valentianae) is a commune in the Nord department, Hauts-de-France, France. It lies on the Scheldt () river. Although the city and region experienced a ...
, Spix, and Agassiz are referred to as ''A. gigas'', though current taxonomy could be revised with more thorough evidence. Currently,
population genetic Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and popu ...
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. There is little debate that ''Heterotis'' is a monotypic genus represented by only ''H. niloticus''. * Arapaiminae Bonaparte, 1846 ** '' Arapaimidarum'' tolith** '' Heterotidinarum'' Nolf, Rana & Prasad 2008 tolith** '' Thrissopterus'' Heckel 1856 ** '' Joffrichthys''? Li & Wilson 1996 ** '' Sinoglossus''? Su 1986 ** '' Heterotis'' Rüppell 1829 ex Ehrenberg 1836 (African arowana) *** '' H. niloticus'' (Cuvier, 1829) ** ''
Arapaima The arapaima, pirarucu, or paiche is any large species of bonytongue in the genus ''Arapaima'' native to the Amazon and Essequibo basins of South America. ''Arapaima'' is the type genus of the subfamily Arapaiminae within the family Osteoglo ...
'' Müller 1843 (arapaima) *** '' A. agassizii'' (Valenciennes, 1847) *** '' A. gigas'' (Schinz, 1822) *** '' A. leptosoma'' Stewart, 2013 *** '' A. mapae'' (Valenciennes, 1847) *** ''A. sp.'' ''
incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertaint ...
''


Description and biology


Description

Arapaimines are characterized by elongate, slender bodies with large scales and long dorsal and anal fins positioned close to a short caudal peduncle. The pelvic fins are small and abdominal if present. They lack chin barbels, have a glossolaryngeal (tongue) bone with teeth present, and the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
e are fixed to the skull. Branched caudal fin rays are less than sixteen, branchiostegal rays between three and seven, and hypurals less than 6. ''Heterotis'' possesses a specialized suprabranchial organ for concentrating and filtering small food particles.


Biology

Both genera make use of similar freshwater habitats in the respective region, with ''Arapaima'' found in the floodplains of the
Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...
and Esequibo river basins of South America and ''Heterotis'' found in littoral zones of large, open rivers in all Sahelo-Sudanese basins of Africa. ''Arapaima'' is typically a top-water fish predator, while ''Heterotis'' is a
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning ...
mud-filterer primarily feeding on phytoplankton and small crustaceans with their suprabranchial organ. Both groups are obligate air-breathers and nest-builders, with males guarding eggs and young.


Evolution

A genetic study shows that Arapaiminae diverged from Osteoglossinae about 220 million years ago, during the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...
. Within Osteoglossinae, the lineage leading to the South American '' Osteoglossum'' arowanas diverged about 170 million years ago, during the
Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations c ...
. The Asian and Australian arowanas in the genus '' Scleropages'' separated about 140 million years ago, during the
Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145  Ma to 100.5 Ma. Geology Pr ...
. Originally, it was thought that the breakup of
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period The Jurassic ( ) is a geologic period and st ...
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 ("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
'' calibrated age of crown-group
Teleostei Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...
, about which fossil and molecular evidence disagree. I.e., hypotheses do not fail only if Teleostei are of
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
origin, but molecular inferences push crown ages further back.


Use by humans

Both ''Arapaima'' and ''Heterotis'' are farmed in their respective regions as relatively large and hardy food-fish.


Etymology

The subfamily is named after the
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
genus ''Arapaima'', whose name derives from the Tupi-Guyarana indigenous name for ''Arapaima gigas''. 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''


References

{{Taxonbar, from1=Q107552925, from2=Q525579, from3=Q18910351 Osteoglossidae Ray-finned fish subfamilies