Iridescent shark

Iridescent shark
Pangasianodon hypophthalmus
Conservation status
Endangered (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Siluriformes
Family:	Pangasiidae
Genus:	Pangasianodon
Species:	P. hypophthalmus
Binomial name
Pangasianodon hypophthalmus (Sauvage, 1878)
Synonyms
Helicophagus hypophthalmus Sauvage, 1878 Pangasius sutchi Fowler, 1937 Pangasius hypophthalmus (Sauvage, 1878)

The iridescent shark (Pangasianodon hypophthalmus) is a species of shark catfish (family Pangasiidae) native to the rivers of Southeast Asia. It is not a shark. It is found in the Mekong basin as well as the Chao Phraya River, and is heavily cultivated for food there. The meat is often marketed under the common name swai. It has also been introduced into other river basins as a food source, and its striking appearance and iridescence have made it popular with fishkeeping hobbyists, among whom it is also known as the Siamese shark or sutchi catfish. The swai's omnivorous diet consists of crustaceans, other fish, and plant matter.

Names

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.

Description

Adults reach up to 130 cm (4 ft) in length and can weigh up to a maximum of 44.0 kg (97 lb). They have a shiny, iridescent color that gives these fish their name. However, large adults are uniformly grey. 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.

Distribution and habitat

P. hypophthalmus migrations in the Mekong River. Orange: March to May
Dark green: May to September
Red: October to February
Shaded region: spawning region of the southern Mekong population between Khone Falls and Kratie

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). 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 in most regions 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. 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; here, it appears to be triggered by receding waters at the end of the flood season.

In August 2015, an environmental group in Santander, Colombia, confirmed that Iridescent sharks had been found in one of the tributaries that feed into the Magdalena river, having been accidentally introduced from illegal farm fisheries in the area. The find has caused alarm amongst the scientific community and government offcicials, as the Magdalena river is home to over 200 native fish species, 35 of which are endangered.

Culinary profile

Swai fillet as sold in the United States

Despite being classified as endangered, iridescent shark is sold cheaply as swai (pronounced /swaɪ/) in the United States or panga in Spain, the second largest importer after Russia. It has a milder flavor and more delicate texture than the U.S.'s native channel catfish. Swai have moist, sweet, mild flavored flesh with a beige color which turns white after cooking. In the U.S. it is often sold as frozen skin-off fillets weighing from 2 oz to 11 oz each. Typical grading sizes are: 3-5 oz, 5-7 oz, and 7-9 oz.

In the aquarium

Pangasianodon hypophthalmus

While juvenile iridescent sharks are sold as pets for home aquariums, they are not easy fish to keep. While they can survive in a 40-gallon aquarium, iridescent sharks are schooling fish that prefer groups, are accustomed to living in rivers, and are active fish that require space. They have very poor eyesight, so detected movement from outside of their habitat can be seen as a threat; If stressed, their first instinct is to flee and such a blind dash can result in injuries 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.

An iridescent shark requires a minimum tank size of 12 m (40 feet) to develop naturally. Schools require even larger tanks. If given enough room and fed adequately, individual fish can reach 1 m (3 feet) in length. In most home aquariums, the lack of space 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 may die prematurely. When provided with adequately-sized aquaria and proper husbandry, an iridescent shark may live into its teens and grow to full size.

See also

• List of freshwater aquarium fish species

External links

• 14 Popular River Fishes in Thai Cooking
• Planet Catfish