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 significance in areas influenced by Chinese culture. The name ''dragon fish'' stems from their resemblance to the Chinese dragon. This popularity has had both positive and negative effects on their status as endangered species.
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 was complete. Genetic studies have confirmed this hypothesis, showing that their ancestor of the Asian arowanas diverged from the ancestor of the Australian arowanas, '''' and '''', 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 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 by German 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 Vietnam, Myanmar, Thailand, Cambodia, and Malaysia.
* The silver Asian 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 area in Perak, Malaysia.
* The red, super red, blood red, or chili red is known only from the upper part of the Kapuas River in western Borneo, Indonesia.
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Description
Asian arowanas grow up to 90 cm . Like all ''Scleropages'', Asian arowanas have long bodies; large, elongate pectoral fins; and anal fins located far back on the body; and a much larger caudal fin than that of their South American relative, the silver arowana, ''Osteoglossum bicirrhosum''. The mouth is oblique with a very wide gape. The prominent lower jaw has two s at its tip. The gill rakers are stout. Asian arowanas bear teeth on many bones of the mouth, including the jaws, vomer, palatines, pterygoids, parasphenoid, and tongue.
Asian arowana scales are large, , and, in some varieties, metallic coloured, with a distinctive mosaic pattern of raised ribs.
Asian arowanas are distinguished from Australian congenerics '''' and '''' by having fewer lateral line scales , longer pectoral and pelvic fins, and a longer anterior snout.
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.
Two breeders reported success using a garden pond measuring by by deep, with pH maintained between 6.5 and 7.0. The fish were over five years old. The successful harvest took place after the third spawning; in the first two spawnings, the male swallowed the eggs, possibly due to improper water quality.
Relationship with humans
Cultural beliefs
Asian arowanas are considered "lucky" by many people, particularly those from . This reputation derives from the species' resemblance to the Chinese dragon, considered an auspicious symbol. The large metallic scales and double barbels are features shared by the Chinese dragon, and the large pectoral fins are said to make the fish resemble "a dragon in full flight."
In addition, positive Feng Shui associations with water and the colours red and gold make these fishes popular for aquariums. One belief is that while water is a place where gathers, it is naturally a source of energy and must contain an "auspicious" fish such as an arowana in order to have balancing yang energy. Another is that a fish can preserve its owner from death by dying itself.
Conservation
The Asian arowanas are listed as by the 2006 IUCN Red List, with the most recent evaluation taking place in 1996. ''S. formosus'' is one of only eight fish species listed on Appendix I. There are a number of registered CITES breeders in Asia and the specimens they produce can be imported into several nations. Other nations restrict or prohibit possession of Asian arowanas; for example, the United States has listed this species under the Endangered Species Act, and therefore it cannot be possessed in that country without a permit.
Declining 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.
There is no recent evaluation of conservation status by IUCN.
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 for at least two generations. The first of these farms was in Indonesia. DNA markers that distinguish among different strains and between sexes have been identified, allowing aquaculturists to identify these characteristics in immature animals.
Care in captivity
Because they can grow up to 90 centimetres long, Asian arowanas require a large aquarium. They are and may be kept with other ''Scleropages'' only in a very large aquarium, provided all fish are of similar size. Like s, they need a tight-fitting cover to prevent jumping. The water should be well-filtred, , and slightly , and maintained at a temperature between 24-30° .
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