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The Asian arowana ( Scleropages formosus) comprises several phenotype varieties of fresh water 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 , slow-moving waters flowing through forested swamps and . Adults feed on other fish, while juveniles feed on .
These popular aquarium fish have special culture 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.
The first description of this species was published in 1840 by German natural history 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 splitting 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 was 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.
Asian arowana scales are large, cycloid scale, and, in some varieties, metallic-coloured, with a distinctive mosaic pattern of raised ribs. The lateral scales are arranged in horizontal rows numbered from the most ventral (first level) to the most dorsal (fifth level), with dorsal scales designated the sixth level.West & NSK (Arowana Club.com), 2003.
Asian arowanas are distinguished from Australian congenerics Scleropages jardinii and Scleropages leichardti by having fewer (21–26) lateral line scales (versus 32–36 for the Australian species), longer pectoral and pelvic fins, and a longer anterior snout.
Green arowanas are dark green on the back, silvery or golden green on its sides, and silvery or whitish on the ventral surface, with dark greenish or bluish patches visible through the lateral scales. In mature fish, the top of the eye and the head behind the eye are bright emerald.
Both grey-tailed and yellow-tailed silver Asian arowanas are dark grey on the back and silver on the sides, with dark ring patches on the lateral scales and a silvery or whitish belly. In yellow-tailed specimens, the fin membranes are yellowish with dark-grey rays. In grey-tailed specimens, the fins are uniformly dark grey.
Mature red-tailed golden arowanas have brilliant metallic gold lateral scales, gill covers, bellies, and pectoral and pelvic fin membranes, although the back is dark. In juveniles, the areas destined to develop golden colour start out metallic silver. The anal fin and the bottom portion of the caudal fin are light brown to dark red.
Mature gold crossback arowanas are distinguished from the red-tailed golden arowanas by having metallic gold crossing the back completely. This variety also lacks the reddish fins of the red-tailed golden. Unoaquatic Arowana Group, 1999.
In mature super red arowanas, the gill covers, lateral scales, and fin membranes of these fishes are metallic red, with the exact hue varying from gold-tinged to deep red. The back is dark brown. In juveniles, the darker the dorsal colouration, the deeper the red will be on maturity.
In Taoist divination, positive feng shui associations with water and the colours red and gold make these fishes popular for aquaria. One belief is that while water is a place where chi gathers, it is naturally a source of yin energy and must contain an "auspicious" fish such as an arowana to have balancing yang energy. Another is that a fish can preserve its owner from death by dying itself.
Declining habitat is a major threat. For example, Asian arowanas are now uncommon in the Malay Peninsula, where they were once widely distributed, due to environmental destruction. Inclusion in the IUCN Red List was originally based not on biological reasons but on practical ones: though widely distributed throughout southeast Asia, they have been harvested heavily by aquarium collectors. However, habitat loss is likely a greater threat than aquarium collecting.
Additionally, considering the current confusion as to number of species, as well as the wide distribution, conservation status should be reconsidered. All strains are probably endangered, but some (notably the super red and red-tailed golden) more critically than others. The Asian arowana's high value as aquarium fish has impacted its conservation. Its popularity has soared since the late 1970s, and hobbyists may pay thousands of U.S. dollars for one of these animals. Certain color varieties are more endangered than others, since the red and gold varieties are both less common, and in higher demand in the aquarium trade.[[File:Scleropages formosus Prague 2012 2.jpg|250px|thumb|In Prague sea aquarium]]
Beginning in 1989, CITES began allowing Asian arowanas to be traded, provided certain criteria were met, most notably that they were bred in captivity on a fish farming for at least two generations. The first of these farms was in Indonesia. Later, the Singapore government's Agri-food and Veterinary Authority (then called the Primary Production Department) and a local fish exporter collaborated in a captive breeding program. Asian arowanas legally certified by CITES for trade became available from this program in 1994.
Captive-bred arowanas that are legal for trade under CITES are documented in two ways. First, fish farms provide each buyer with a certificate of authenticity and a birth certificate. Second, each specimen receives an implanted microchip, called a passive integrated transponder, which identifies individual animals.
Genetic fingerprinting has been used to assess the genetic diversity of a captive population at a Singapore fish farm to improve the management of this species. DNA markers that distinguish among different strains and between sexes have been identified, allowing aquaculturists to identify these characteristics in immature animals.
According to author Emily Voigt, the arowana has been cause for kidnappings, canings and even murder.
Asian arowanas are carnivore and should be fed a high-quality diet of meaty food, such as shrimp and crickets. They are surface feeders and prefer to take food in the upper parts of the water column. Aquarists recommend live foods and meaty prepared foods. Examples of appropriate live foods include , centipedes, , crickets, , feeder fish, small , and . Prepared foods include prawns (shrimp), lean pork, frozen fish food, and pelleted food. Anglo Aquarium (n.d.); Shin Min Daily News, 2005 Some captive arowanas are fed Koi fry in an attempt to increase the vibrancy of their natural coloration.
There are over 150 CITES-registered Asian arowana farms in Singapore, Malaysia, Indonesia and other Southeast Asia countries, producing Asian arowana for commercial purposes. But the actual number of Asian arowana farms in the world could be much higher than that, and probably over 350, of which most may not be registered in CITES yet. The total annual revenue of the Asian arowana sector was estimated at over US$200 million globally.
Possession of Scleropages formosus by private citizens is prohibited in Florida and New Mexico.
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