Sutchi Catfish

Sutchi Catfish Despite its name, iridescent shark, Pangasius hypophthalmus is not a shark, but a catfish. This fish is also known as Siamese shark or sutchi catfish in the aquarium hobby or as tra, swai, or striped catfish in the food fish market, and occasionally incorrectly as basa and panga (though these names should be rather used for Pangasius bocourti and Pterogymnus laniarius, respectively). The species is found in Southeast Asia 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 is common in the fishkeeping hobby. It is named for its glow or iridescence exhibited in juveniles. Their omnivorous diet consists of crustaceans, other fish, and plant matter.[3] Distribution and habitat 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 to 29.0 dGH, and a temperature range of 72 to 79 °F (22 to 26 °C).[3] 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.[3] [edit] Physical Characteristics 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).[3] Food source Swai fillet as sold in the United States (top and bottom)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[3] 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" (its Thai name[citation needed]), "sutchi catfish", or "striped catfish". In Vietnam, this fish is known as "tra".[4] 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. It is said that 90% of fish sold as basa is actually swai.[4] [edit] In the aquarium Juvenile iridescent sharks are often sold as pets for home aquariums. However they are not easy fish to keep and are not recommended for most home aquariums. Iridescent sharks are schooling fish that prefer to be kept in groups of 5 or more.[3] 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.[5] Many fish owners are unaware of the enormous size that an iridescent shark can reach. 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. It's for this reason that 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.[dubious discuss] As a rule of thumb, an iridescent shark requires a minimum tank size of 3 m (10 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.[6] There is also an albino morph available.[6]