Asian arowana
From Wikipedia, the free encyclopedia
[Photo] Arowana (Scleropages formosus) Source: Fotografiert von Marcel Burkhard alias cele4 Template:FPC
Asian arowana refers to several varieties of freshwater fish in the genus Scleropages. Some sources differentiate these varieties into multiple species[2], while others consider the different strains to belong to a single species, Scleropages formosus.[3] They have several other common names, including Asian bonytongue, dragon fish, and a number of names specific to different varieties (see Description below).
Native to Southeast Asia, Asian arowanas inhabit blackwater rivers, slow-moving waters flowing through forested swamps and wetlands. Adults are piscivorous, with juveniles feeding on insects.[4]
These popular aquarium fish have special cultural significance in areas influenced by Chinese culture. The name dragon fish stems from their resemblance to the mythical Chinese dragon. This popularity has had both positive and negative effects on their status as endangered species.
Origin
All osteoglossids are highly adapted to freshwater and are incapable of surviving in the ocean; therefore, the spread of Asian arowanas throughout the islands of southeast Asia suggests they diverged from other osteoglossids before the continental breakup was complete. Confirmation has come from genetic studies, which have shown 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 six species shows that little evolutionary change has taken place recently for these ancient fish.
Description
The first description of these species was published between 1839 and 1844 (1844 is the date commonly cited) by German naturalists Salomon M??ller and Hermann Schlegel, under the name Osteoglossum formosum, although later this species was placed in Scleropages with the name S. formosus.
Strains
Prior to 2003, all Asian arowanas were placed in this species, with several distinct color varieties recognized. These strains occur naturally and are based on geographic region; they include the following:
The green is the most common variety, found in Vietnam, Myanmar, Thailand, and Malaysia.
The silver Asian (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 Bukit Merah 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.
However, in 2003, a study[7] 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.
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.[8]
Asian arowanas are prized aquarium fish in some parts of the world, and the various color varieties have differing values to hobbyists. The super red arowana is regarded by many to be of greatest beauty because red is considered an auspicious color, according to some local cultures (see Cultural Beliefs below). Each color variety has variations among different localities. For instance, the gold crossback may have various base colours, including blue, gold, green, turquoise, and purple. Hobbyists consider the highest grade of the gold crossback to be the full gold crossback (frameless gold), which originated from the Sungai Gedong river system.
Appearance
Asian arowanas grow up to 90 cm (35 in) total length.[9] Like all Scleropages, Asian arowanas have long bodies; large pectoral fins; dorsal 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. These mouthbrooding carnivores have paired barbels on the end of the lower jaw.[10]
Asian arowana scales are large and, in some species, metallic colored, with a distinctive network of raised ribs.[11] 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.[12]
All Asian arowanas are distinguished from Australian congenerics S. jardinii and S. 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.[13]
Green arowanas are dark green on the back, silvery or golden green on its sides, and silvery or whitish on its 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. The green arowana is the only one of the four species to have the combination of a narrow head and long upper jaw (maxillary); it also has a short anal fin.[14]
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 uniform dark grey. Silver Asian arowanas are distinguished by having the broadest heads of all the Asian arowanas. They also have long maxillaries and short anal fins.
Mature red-tailed golden arowanas have brilliant metallic gold lateral scales, opercula, bellies, and pectoral and pelvic fin membranes, although the back remains dark in color. In juveniles the areas destined to develop golden color start out metallic silver. The anal fin and the bottom portion of the caudal fin are light brown to dark red in color. Red-tailed golden arowanas have shorter upper jaws (maxillaries) than green and silver Asian arowanas, as well as the longest anal fins of the four species.[16]
In mature super red arowanas, the opercula, 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 coloration, the deeper the red hue will be on maturity. Red arowanas have the shortest maxillaries of the four species as well as short anal fins.
Mature specimens gold crossback arowanas are distinguished in terms of color 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.
Reproduction
All species of arowanas are paternal mouthbrooders. Slow to reach sexual maturity, they are difficult to breed in captivity, with successful spawnings typically taking place in large outdoor ponds rather than in aquariums.[19] One breeder reported success using a garden pond measuring 18 ft by 18 ft by 3.5 ft deep (5.5 m by 5.5 m by 1.1 m 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.
Cultural beliefs
Asian arowanas are considered "lucky" fish by many people, particularly those from Asian cultures. This reputation derives from the species' resemblance to the Chinese dragon, considered an auspicious symbol.[21] When one of these fishes swims, its large pectoral fins spread out, which is said to make it resemble "a dragon in full flight."[22] The species' large metallic scales and double barbels are features shared by the Chinese dragon; some people believe the Asian arowana is a reincarnation of the dragon. In addition, positive Feng Shui associations with water and the colors red and gold make these fishes popular for aquariums.
One belief associated with Asian arowanas 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 in order to have balancing yang energy.[23] Another is that a fish can preserve its owner from death by dying itself.[24]
Conservation status
The Asian arowanas are listed as endangered by the 2006 IUCN Red List, although it was last evaluated in 1996.[25] International trade in these fishes is controlled under the Convention on the International Trade in Endangered Species of Wild Flora and Fauna (CITES), under which it was placed on Appendix I, the most restrictive category, in 1975.[26][27] S. formosus is one of only eight fish species listed on Appendix I. [28] There are twenty three registered CITES breeders in Asia and the specimens they generate can be imported into several nations, although not the United States.
In light of the recent reclassification into four species, conservation status needs to be reconsidered. All are probably endangered, but some species are more critically endangered than others.[29] In addition, S. formosus has not been evaluated by IUCN since 1996.
Farming and the aqarium trade
These species' wild stocks have been depleted largely due to their high value as aquarium fish. Their popularity has soared since the late 1970s, and today hobbyists may pay tens of thousands of Philippine pesos, or thousands of U.S. dollars, for one of these animals.[30]
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 farm for at least two generations.[31] The first of these was in Indonesia.[32] 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.[33]
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 (PIT), which identifies each individual fish.[34]
Genetic fingerprinting has been used to assess the genetic diversity of a captive population at a Singapore fish farm in order to improve the management of this species.[35] DNA markers that distinguish among different strains and between sexes have been identified, allowing aquaculturists to identify these characteristics in immature animals.[36]
Asian arowanas as aquarium fish
Asian arowanas are large fish and require a large aquarium. They are carnivores and should be fed a high-quality diet of meaty food, such as shrimp and crickets. These territorial fish should not be kept with other Scleropages except in a very large aquarium. Prized specimens can cost thousands of dollars. Greens are the least valuable, followed by red-tail goldens, crossback goldens, and reds.
Adult arowanas are territorial, but can be kept together with tankmates of similar size. Like other arowanas, they are strong jumpers.[37]
Because they can grow up to 90 cm (35 in.) long, Asian arowanas require a large tank, with a tight-fitting cover to prevent jumping. The water should be well-filtered, soft, and slightly acidic, and maintained at a temperature between 24-30° C (75-86° F).[38]
Asian arowanas are surface feeders and prefer to take food in the upper parts of the water column. Hobbyists familiar with these fishes recommend live foods and other meaty foods. Examples of appropriate live foods include mealworms, crickets, shrimps, feeder fish, small frogs, and earthworms. Prepared foods include prawns (shrimp), lean pork, frozen fish food, and pelleted food. Prawns can enhance red coloration. [39]
| The text in this page is based on the copyrighted Wikipedia article shown in above URL. It is used under the GNU Free Documentation License. You may redistribute it, verbatim or modified, providing that you comply with the terms of the GFDL. |
|
