Scleropages formosus

The Asian arowana (Scleropages formosus) comprises several phenotypic varieties of freshwater fish distributed geographically across Southeast Asia. While most consider the different varieties to belong to a single species, work by Pouyaud et al. (2003) differentiates these varieties into multiple species. They have several other common names, including Asian bonytongue, dragonfish, and a number of names specific to the different color varieties. Native to Southeast Asia, Asian arowanas inhabit blackwater rivers, slow-moving waters flowing through forested swamps and wetlands. Adults feed on other fish, while juveniles feed on insects. These popular aquarium fish have special cultural significance in areas influenced by Chinese culture. The name 'dragonfish' stems from their resemblance to the Chinese dragon. This popularity has had both positive and negative effects on their status as endangered species. Like all members of the 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 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 little evolutionary change has taken place recently for these ancient fish. The first description of this species was published in 1840 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 as haplotypes, each found in a specific geographic region. They include: In 2003, a study proposed breaking S. formosus into four separate species. This classification was based on both morphometrics and a phylogenetic analysis using the cytochrome b gene, and includes these species: The majority of researchers dispute this reclassification, arguing that the published data are insufficient to justify recognizing more than one Southeast Asian species of Scleropages, and that divergent haplotypes used to distinguish the color strains into isolated species were found within a single color strain, contradicting the findings. They are considered monotypic, consisting of closely related haplotypes.