The iridescent shark is a shark catfish that is a native to the rivers across Southeast Asia. They are not really sharks. They do, however, look very similar to small sharks. They are found over Mekong Basin and the Chao Phraya River areas and used for food there. The fish are marketed as swai in the United States. They are very similar to the US catfish.
Iridescent shark
Features
The pangasius has the scaleless, elongated body typical of the shark catfish (Pangasiidae). Adult animals reach a maximum weight of 44 kilograms at a length of up to 150 centimeters. They are dark grey with a lighter belly and dark grey to black fins. Very old and large animals become uniformly gray. As characteristic features of the genus Pangasianodon, the Pangasius has a terminal mouth (upper and lower jaws are therefore of equal length), a swim bladder with only one lobe and ventral fins with eight, rarely nine soft rays. In adults, the mouth is also toothless and the barbels on the lower jaw are missing. It differs from the other species of the genus, the Mekong Giant Catfish, by its much smaller size as well as the less broad head and the construction of the gill trap, which is well developed in the Pangasius and carries about 40 very short rays on the first arch between 15 longer rays.
The dorsal fin has, as in many catfish, a spiny hard ray followed by six branched soft rays. An adipose fin is present. The anal fin is elongated on the belly and has a black stripe in the middle, as do both lobes of the caudal fin. The small pelvic fins are located just in front of the anal fin.
Newly hatched individuals are yellowish and almost translucent with distinct barbels, while older juveniles resemble adults and have a black stripe along the lateral line organ and another just below. This pattern fades with age.
The chromosome set consists of 30 pairs (2n = 60).
Occurrence
The species inhabits the major river courses of the Mekong and Mae Nam Chao Phraya (Chao Phraya River) in Thailand, Vietnam, Laos and Cambodia. The Mekong River occurrence is believed to be divided into a southern population in Cambodia and Vietnam and a northern population in Laos and Thailand by the waterfalls in the Lao province of Champasak. Catches in the area of the falls, however, indicate some exchange between populations. More detailed genetic studies are only available on the southern population, within which there are three co-occurring, genetically distinct subpopulations, possibly separated by different spawning seasons. The spawning area of the southern Mekong population is in a relatively small area in northern Cambodia between Kratie and the Mekong Falls; that of the northern and Chao Phraya populations is unknown.
In Bangladesh, Singapore and the Philippines, naturalized stocks exist as a result of the introduction to aquaculture. Here the species is considered ecologically very problematic due to its voracity and possible competition with native fish.
