Scleropages

These species are highly valued as aquarium fish, particularly by those from Asian cultures. In 2003, a study redescribed several naturally occurring color varieties of S. formosus into four separate species. The majority of researchers dispute these redescriptions, 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 based on color. == Evolution ==

The unusual distribution of arowanas in both Asia and Australia (last connected during the Mesozoic), despite their freshwater habits, is unique and the subject of several competing hypotheses about when the ancestor of the Australian arowanas diverged from the ancestor of the Asian arowanas. Kumazawa & Nishida (2000) hypothesized that the two clades diverged about 140 million years ago, during the Early Cretaceous period, as a product of continental vicariance, when Insular India (containing the Asian Scleropages) & Madagascar broke off from the Australian & Antarctic landmass, fragmenting a population of ancestral Scleropages that inhabited East Gondwana during the Early Cretaceous. Lavoue (2015) also found evidence for a Cretaceous divergence between these two clades, but found it to post-date the fragmentation of East Gondwana, suggesting that the ancestral Scleropages dispersed over marine habitats to its present range during the Late Cretaceous. More recently, Cioffi et al (2019) firmly found that the divergence between the Asian and Australian arowanas only dates to the late Eocene, about 35 million years ago, suggesting that the current distribution of Scleropages is best explained by a late Paleogene marine dispersal between Asia and Australia, followed by extirpation of the genus in marine habitats, leaving only the freshwater species. However, fossils of this genus have not yet been definitively identified from marine deposits. The genus had a much wider distribution during the early Cenozoic, with fossil remains known from the Paleocene of Niger and Belgium, and from the Eocene of China and Indonesia. ==Species==

There are currently 4 recognized species in this genus: The following fossil species are also known: • †Scleropages sanshuiensis Zhang, 2020 (Early Eocene of Guangdong, China) • †Scleropages sinensis Zhang & Wilson, 2017 (Early Eocene of Hunan & Hubei, China) In addition to these two fossil species known from complete skeletons, fossil remains of indeterminate Scleropages are also known from Middle Paleocene-aged freshwater deposits of Belgium, Late Paleocene-aged freshwater deposits of Niger, the Eocene-aged freshwater Sangkarewang Formation of Sumatra, Indonesia, and Neogene-aged deposits of Australia. The genus may potentially date to the Late Cretaceous, as fossil osteoglossid otoliths from the Maastrichtian-aged Intertrappean Beds of India closely resemble those of this genus, as does a partial jaw with teeth from the Campanian of France. ==Phylogeny==

Phylogeny based on the work of Pouyaud, Sudarto & Teugels 2003. }} ==References==