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| Wallago attu | |
|---|---|
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Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Siluriformes |
| Family: | Siluridae |
| Genus: | Wallago |
| Species: | W. attu |
| Binomial name | |
| Wallago attu | |
| Synonyms | |
Silurus boalisHamilton, 1822 | |
Wallago attu, theboal orhelicopter catfish is afreshwater catfish of the familySiluridae, native toSouth andSoutheast Asia.W. attu is found in large rivers and lakes in two geographically disconnected regions (disjunct distribution), with one population living over much of theIndian Subcontinent and the other in parts ofSoutheast Asia. This species can reach a length up to 1.1 m (3 ft 7 in).[2]
It shares parts of its native range with the externally similar, but much largerWallagonia leerii, and is subsequently often confused for it. It can, however, be differentiated by its relatively long and narrower head, as well as its dorsal fin, which is high and sharp, opposed to that ofW. leerii, which is lower and rounded. Additionally, the eyes ofW. attu lie above the mouth of the fish, whilst they lie on the same level as the mouth inW. leerii.
This catfish is one of the fish species that has been used as food in Southeast Asia since ancient times.[3] In Thailand, its meat is popularly used to makethot man (ทอดมัน, "Thaifish cakes"), similar toclown featherback (Chitala ornata).[4]
In many areas,Wallago attu is found alongside the externally similar and related catfish speciesWallagonia leerii. In Indonesia and Malaysia, both species are referred to asikan tapah, and in English, both are sometimes calledhelicopter catfish. Popular accounts such as media reports, claims by fishermen, or local folklore stories, and even scientific publications, often confuse the two or are altogether unaware of the difference. Therefore, claims exist thatWallago attu reaches lengths of more than 1.8 m (5 ft 11 in) and weights of more than 45 kg (99 lb).[5] Biologists, however, are firm that it does not grow beyond a length of roughly 1 m (3 ft 3 in).[2] The current rod-and-reel angling record for aWallago attu caught in the wild and authenticated by theInternational Game Fish Association is a specimen of 18 kg (40 lb) from theVajiralongkorn dam reservoir in Thailand, while some specialized recreational catch-and-release breeding ponds in the region claim to harbour specimens in the 20–30 kg (44–66 lb) range.[6][7] It is thus assumed that reports about specimens even larger than that actually refer toWallagonia leerii, which can grow to twice the length and several times the weight ofWallago attu.
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Wallago attu lives through large parts ofSouth andSoutheast Asia. Its range, however, seems discontiguous with a significant gap between the population inhabiting the Indian subcontinent and the one found across mainland and insular Southeast Asia.W. attu thus stands as an example for a species with adisjunct distribution.[2]
On theIndian subcontinent, its range includes all the major rivers of India, Pakistan, Bhutan, Nepal and Bangladesh, such as theGanges,Indus,Narmada,Godavari,Krishna andMahanadi as well as the island of Sri Lanka. To the Northwest, its range extends beyond Pakistan into Iran and Afghanistan. To the East, it can be found as far as theIrrawaddy river basin in Myanmar.[2][8][9][10][11][12]
The second population occurs in Southeast Asia and encompasses Thailand, Laos, Cambodia, Vietnam, Malaysia and Indonesia. Here it inhabits theMae Klong,Chao Phraya andMekong drainages, as well as those of theMalayan peninsula and the islands ofJava andSumatra. It is absent fromBorneo, which ichthyologistTyson R. Roberts considers "surprising".[2]
The gap between the two populations is largely formed by theSalween andTenasserim River drainages in Burma, whereW. attu is not found. The reasons for this disjunct distribution are unknown.[2]
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As a large, predatory fish,W. attu maintains a largelypiscivorous diet. Gut content analysis performed on specimens from the Godavari river in India shows that about 90 to 95% of the consumed food consisted of animal matter. Among the prey fishes most commonly found in the stomachs of Godavari riverW. attu arerazorbelly minnows (Salmophasia phulo),ticto barbs (Pethia ticto) andperchlets (Chanda nama), all of which are small species that reach maximum lengths of about 10–12 cm (3.9–4.7 in).[8]
The vast and disjunct distribution ofW. attu has led to the assumption that it might in fact not be a single species. A preliminary bone-by-bone comparison ofW. attu specimens from Southeast Asia and South Asia showed significant differences in their skeletal structure. It is thus assumed that pending further researchW. attu may possibly be split into two or more species within the genusWallago in the future.[2]
According to Malaysian folklore, the descendant of a person called Tok Kaduk cannot eat and touch the fish because the legend says that a long time ago, Tok Kaduk caught thistapah. When he cut open its stomach, there was gold inside the fish so Tok Kaduk took the gold, stitched up the fish, and released it back into the river. From that time, if the descendant came in touch with the fish, their skin would become red and itchy until they went to Kg Tua, Lambor Kanan near Bota inPerak Tengah District ofPerak, Malaysia to find the medicine. The medicine is the remaining gold from the fish, which has been kept to make the cure for the disease. Some say that the gold needs to be soaked in water and consumed by the patient as well as washing the areas that itch. Other stories have told that fish will devour the carcass of humans that have been buried in the water, and it will take the human's soul to the gods.[13]
The Malaysian town ofTapah and differenttropical storms named Tapah have been named after this fish (or the identically namedWallagonia leerii).
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