Asian Arowana - Evolution and Taxonomy

Evolution and Taxonomy

Like all members of Osteoglossidae, Asian arowanas are highly adapted to fresh water and are incapable of surviving in the ocean. Therefore, their spread throughout the islands of southeast Asia suggests they diverged from other osteoglossids before the continental breakup was complete. Genetic studies have confirmed this hypothesis, showing that the ancestor of the Asian arowanas diverged from the ancestor of the Australian arowanas, S. jardinii and S. leichardti, about 140 million years ago, during the Early Cretaceous period. This divergence took place in the eastern margin of Gondwanaland, with the ancestors of Asian arowanas carried on the Indian subcontinent or smaller landmasses into Asia. The morphological similarity of all Scleropages species shows that little evolutionary change has taken place recently for these ancient fish.

The first description of these species was published between 1839 and 1844 (1844 is the date commonly cited) by German naturalists Salomon Müller and Hermann Schlegel, under the name Osteoglossum formosum, although later this species was placed in Scleropages with the name S. formosus.

Several distinct, naturally occurring colour varieties are recognised, each found in a specific geographic region. They include the following:

  • The green is the most common variety, found in Indonesia (Kalimantan and Sumatra), Vietnam, Myanmar, Thailand, Cambodia, and Malaysia.
  • The silver Asien (not to be confused with the silver arowana, Osteoglossum bicirrhosum) is considered part of the green variety by some. It has two subvarieties, the "grey tail silver" or "Pinoh arowana," and the "yellow tail silver," each found in a different part of the island of Borneo in Indonesia.
  • The red-tailed golden is found in northern Sumatra, Indonesia.
  • The gold crossback, blue Malayan, or Bukit Merah blue is native to the state of Pahang and the Bukit Merah area in Perak, Peninsular Malaysia.
  • The red, super red, blood red, or chili red is known only from the upper part of the Kapuas River and nearby lakes in western Borneo, Indonesia.

In 2003, a study was published which proposed breaking S. formosus into four separate species. This classification was based on both morphology and genetics, and includes the following species:

  • Scleropages formosus was redescribed to include the strain known as the green arowana. The gold crossback, which was not part of the study, was included in this species by default, though it was suspected that it was closely related to S. aureus.
  • Scleropages macrocephalus described the silver Asian arowana.
  • Scleropages aureus described the red-tailed golden arowana.
  • Scleropages legendrei described the super red arowana.

Other researchers dispute this reclassification, arguing that the published data are insufficient to justify recognizing more than one Southeast Asian species of Scleropages.

Read more about this topic:  Asian Arowana

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