| Iridescent shark | |
|---|---|
| Pangasius hypophthalmus | |
| Conservation status | |
|
NE[1]
|
|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Siluriformes |
| Family: | Pangasiidae |
| Genus: | Pangasius |
| Species: | P. hypophthalmus |
| Binomial name | |
| Pangasius hypophthalmus (Sauvage, 1878) |
|
| Synonyms | |
|
Pangasius sutchi Fowler, 1937[2] Pangasianodon hypophthalmus Sauvage |
|
The iridescent shark (Pangasius hypophthalmus) is a species of shark catfish (family Pangasiidae) native to the rivers of Southeast Asia. It is found in the Mekong basin as well as the Chao Phraya River, and is heavily cultivated for food there. It has also been introduced into other river basins as a food source, and its striking appearance and iridescence have made it common in the fishkeeping hobby. Their omnivorous diet consists of crustaceans, other fish, and plant matter.[4]
Contents |
The fish is named for the glow or iridescence exhibited in juveniles, as well as the shark-like appearance of this and other shark catfish. It is also known as Siamese shark or sutchi catfish in the aquarium hobby or as tra, sawai (Thai: ปลาสวาย), or striped catfish in the food fish market, and occasionally incorrectly as basa and panga (these names should be rather used for Pangasius bocourti and Pterogymnus laniarius, respectively).
Iridescent sharks originate from the large rivers Chao Phraya and Mekong in Asia, though they have been introduced into other rivers for aquaculture. They are a freshwater fish that natively live in a tropical climate and prefer water with a 6.5–7.5 pH, a water hardness of 2.0–29.0 dGH, and a temperature range of 22–26 °C (72–79 °F).[4] They prefer large bodies of water similar to the deep waters of their native Mekong river basin.
The iridescent shark is a migratory fish that moves upstream to spawn during the flood season while the waters are high and returns downstream to seek rearing habitats when the river water levels recede. Upstream migration in this species appears to be triggered by receding waters. At the end of the flood season, the fish migrate back downstream away from flooded waters. The dates of the migrations vary depending on the river system. In the Mekong river basin, they migrate upstream in May to July and return downstream during September through December. South of the Khone Falls, upstream migration occurs in October to February, with its peak in November to December.[4]
The fins are dark grey or black. Juveniles have a black stripe along the lateral line and a second black stripe below the lateral line; they have a shiny, iridescent color that gives these fish their name. However, large adults are uniformly grey and lack the striping. Adults reach up to 130 cm (4 ft) in length and can weigh up to a maximum of 44.0 kg (97 lb).[4]
P. hypophthalmus is an important food fish and is farmed extensively in many parts of the world. It is one of the most important aquaculture species in Thailand[4] and Vietnam. Along with other farm-raised shark catfishes, it has caused much debate within the U.S., with legislation passed recently to prevent its imports from cutting into American farmed catfish sales. Prohibited to be labelled as "catfish" in the U.S., P. hypophthalmus is now labelled as "swai", a corruption of its Thai name, or "striped catfish" (formerly "sutchi catfish"). In Vietnam, this fish is known as tra.[5] In Mexico, Grupo Piscimex markets this fish with the registered trademark "Barbero" under the brand name "Pescados y Mariscos Sierra Madre." Other than indicating the Latin name of the species on the back and that it was farm-raised in Vietnam, they make no mention of its more common names.
This fish is sometimes sold as the superior "basa". Compared to the basa, this fish is thought to be inferior, as its meat is coarser and comes in thinner. Despite this, swai is still common, as it is much cheaper to maintain, easier to breed, and is also a faster-growing species. Since consumers in Vietnam prefer basa, owing to their more delicate flake and sweeter flavor, and since swai grows more quickly, more swai is shipped to US markets than basa.[6]
Juvenile iridescent sharks are often sold as pets for home aquariums. However, they are not easy fish to keep, and are not recommended for home aquariums. Iridescent sharks are schooling fish that prefer to be kept in groups of five or more.[4] Accustomed to living in rivers, they are very active fish that require a lot of space. They have very poor eyesight, so any foreign movement they detect outside of their habitat, they will see as an utter threat. If stressed, their first instinct is to flee, and such a blind dash can result in injuries, especially in an aquarium environment. These flights may be terminated by the fish sinking to the bottom, where it may lie on its side or back until it recovers.[7]
Many fish owners are unaware of the enormous size an iridescent shark can reach and also that they can bite very harshly. If given enough room and fed adequately, an individual of this species can reach 1 m (3 feet) in length. In most home aquariums, the amount of space an iridescent shark has severely stunts its growth. For this reason, most iridescent sharks kept in home aquaria grow to only 15 to 30 cm (6 to 12 inches) in length and die prematurely from organ failure. As a rule of thumb, an iridescent shark requires a minimum tank size of 12 m (40 feet) to develop naturally and live a long, healthy life. Schools require even larger tanks. When provided with adequate sized aquaria and proper husbandry, an iridescent shark may live well into its teens and grow to full size.[8]
There is also an albino morph available.[8]