Arowana


Osteoglossinae are a subfamily of freshwater bony fish, commonly known as arowanas or bonytongues. The name "bonytongues" is derived from a toothed bone on the floor of the mouth, the "tongue", equipped with teeth that bite against teeth on the roof of the mouth. In this family of fish, the head is bony and the elongated body is covered by large, heavy scales, with a mosaic pattern of canals. The dorsal and anal fins have soft rays and have long fin origins, while the pectoral and ventral fins have stiffer, longer rays. Arowanas are facultative air breathers and can obtain oxygen by ingesting air into its swim bladder, which is lined with capillaries like lung tissue. Despite this, they are not considered amphibious.
The two genera each inhabit a different continent despite its members being freshwater fish, which suggests vicariance from the breakup of Gondwana.

Nomenclature

The name comes from the Tupí language arua'ná, aruanã, or arauaná.

Taxonomy

  • Subfamily Osteoglossinae Bonaparte, 1831
  • * Genus Scleropages Günther, 1864
  • * Genus Osteoglossum Agassiz ex Spix & Agassiz, 1829 non Basilewsky, 1855

    Evolution

At least five extinct genera, known only from fossils, are classified as osteoglossids; these date back at least as far as the Late Cretaceous. Other fossils from as far back as the Late Jurassic or Early Cretaceous are widely considered to belong to the arowana superorder Osteoglossomorpha. Osteoglossomorph fossils have been found on all continents except Antarctica. These fossil genera include Brychaetus, Joffrichthys, and Phareodus.
Within Osteoglossinae, the South America Osteoglossum arowanas diverged from the Asian and Australian Scleropages arowanas about 170 Mya, during the Middle Jurassic.
Osteoglossidae are the only exclusively freshwater fish family found on both sides of the Wallace Line. This may be explained by the theory that Asian arowanas diverged from the Australian Scleropages, S. jardinii and S. leichardti, about 140 Mya, making it likely that Asian arowanas were carried to Asia on the Indian subcontinent.

Behavior

Osteoglossids are carnivorous, often being specialized surface feeders. They are excellent jumpers; Osteoglossum species have been seen leaping more than from the water surface to pick off insects and birds from overhanging branches in South America, hence the nickname "water monkeys." Arowana species typically grow to around in captivity.
Several species of osteoglossids exhibit parental care. They build nests and protect their young after they hatch. All species are mouthbrooders, the parents holding sometimes hundreds of eggs in their mouths. The young may make several tentative trips outside the parent's mouth to investigate the surroundings before leaving permanently. Unlike most fishes that start reproducing at around six months of age, the arowana usually takes three to four years to reach sexual maturity.

In the aquarium

Depending on the classification system used, there are ten types of arowana commonly kept as pets: four from Asia, three from South America, two from Australia, and one from Africa.
Asian arowana is an endangered species and banned in the United States. It is a status symbol among wealthy Asian men. An albino arowana sold for a record price of $300,000 in 2009. Most pet arowana are farmed behind high-security fences. It is estimated that the total annual revenue of the Asian arowana sector was over US$200 million globally since 2012.
Arowanas are solitary fish and only allow company while young; adults may show dominance and aggression. Some compatible species often partnered with this fish are clown knifefish, pacu, oscars, jaguar cichlids, green terrors, gar, tinfoil barb, Siamese tigerfish, and any other somewhat aggressive fish that cannot fit in the arowana's mouth. These fish are best kept with live or frozen feed and they easily outgrow the tank within eight to ten months. An aquarium with the minimum diameter of and is suggested as a bare minimum but is the best way to go. Australian species are best kept alone in aquaria.