The Mekong giant catfish (Pangasianodon gigas; , , ; /trəy riec/; ), is a large, threatened species of catfish (order Siluriformes) in the shark catfish family (Pangasiidae), native to the Mekong basin in Southeast Asia and adjacent China. It is considered critically endangered due to overfishing and habitat loss.
Description
Grey to white in color and lacking stripes, the Mekong giant catfish is distinguished from other large catfish species in the river by the near-total lack of barbels and the absence of teeth. Young Mekong catfish do exhibit barbels and oral teeth, but these features diminish as they age and are absent by the time they grow to be 30-50cm in length.
Mekong giant catfish are one of the largest species of freshwater fish. In 2005, the Mekong giant catfish attained the Guinness World Record for the world's largest freshwater fish. Attaining a length of up to , the Mekong giant catfish grows extremely quickly, reaching a mass of in only six years. It can reportedly weigh up to . The largest catch recorded in Thailand since record-keeping began in 1981 was a female measuring in length and weighing . This specimen, caught in 2005, was widely recognized as the largest entirely freshwater fish ever caught (the largest sturgeon species can far exceed this size, but they are anadromous), until surpassed in June of 2022 by a giant freshwater stingray specimen caught in Cambodia. Thai fisheries officials stripped the giant catfish, caught in 2005, of its eggs as part of a breeding program, intending then to release it, but the fish died in captivity and was sold as food to local villagers.
Distribution and habitat
The Mekong giant catfish is a threatened species in the Mekong, and conservationists have focused on it as a flagship species to promote conservation on the river. Although research projects are currently ongoing, relatively little is known about this species. Historically, the fish's natural range reached from the lower Mekong in Vietnam (above the tidally influenced brackish water of the river's delta) all the way to the northern reaches of the river in the Yunnan Province of China, spanning almost the entire length of the river. Due to threats, this species no longer inhabits the majority of its original habitat. It is now believed to only exist in small, isolated populations in the middle Mekong region. Fish congregate during the beginning of the rainy season and migrate upstream to spawn. They live primarily in the main channel of the river, where the water depth is over , while researchers, fishermen and officials have found this species in the Tonle Sap River and Lake in Cambodia, a UNESCO Biosphere Reserve. In the past, fishers have reported the fish in a number of the Mekong's tributaries. Today, however, essentially no sightings are reported outside of the main Mekong river channel and the Tonle Sap region. A 150 kg individual was found in a Kelantan river in Malaysia, it is believed to have been released illegally.
Understanding of the species’ migration pattern is incomplete. The fish are thought to rear primarily in the Mekong and Cambodia's Tonle Sap lake and migrate hundreds of miles north to spawning grounds in Thailand. Spawning fish in the upper Cambodia are being over harvested. Fragmentation caused by infrastructure development of dams are becoming increasingly common posing threats to larval fish and reducing breeding abilities. Overfishing, damming, destruction of spawning, and breeding grounds and siltation have taken a toll on the species' habitat.
Feeding
As fry, this species feeds on zooplankton in the river and is known to be cannibalistic. After about one year, the fish becomes herbivorous, feeding on filamentous algae, probably ingesting larvae and periphyton accidentally. The fish likely obtains its food from algae growing on submerged rocky surfaces, as it does not have any sort of dentition. The Mekong giant catfish are toothless herbivores that live off of the plants and algae in the river. One scientific study found zooplankton and phytoplankton in their stomach contents.
In captivity
Mekong giant catfish are now successfully bred in Thailand, they are often hybridised with the iridescent shark to make the Mekong iridescent shark. They also have a short body form like the paroon shark and iridescent shark. They are also bred for the aquarium trade. Ownership and importation of the fish has been restricted in various states of Australia due to fears it could become an invasive species.