The Mekong giant catfish is perhaps the most interesting and most threatened species in the Mekong river. For this reason conservationists have chosen it as a sort of “flagship” species to promote conservation on the Mekong. With recorded sizes of up to 10.5ft (3.2m) and 660lb (300kg), the Mekong’s giant catfish currently holds the Guinness Book of World Record’s position for the world’s largest freshwater fish. Although research projects are currently on going, relatively little is known about this species. Historically, the fish has a natural range that reaches 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 4,800 km length of the river. Due to threats this species no longer inhabits the majority of its original habitat, now believed to only exist are small, isolated populations in the middle Mekong region. Fish congregate during the beginning of the rainy season and migrate up-stream to spawn. They live primarily in the main channel of the river where the water depth is over 10m 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 fishermen have reported the fish in a number of the Mekong’s tributaries, however today essentially no sightings are reported outside of the main Mekong river channel and the Tonle Sap region.
In infancy, this species feeds on zooplankton in the river and is known to be cannibalistic. After approximately one year, the fish becomes herbivorous, feeding on filamentous algae probably ingesting larvae and periphyton accidentally. The fish likely obtain their food from algae growing on submerged rocky surfaces, as they do not have any sort of dentition.
Endemic to the lower half of the Mekong river, this catfish is in danger of extinction due to overfishing, as well as the decrease in water quality due to development and upstream damming. The current IUCN Red List for fishes classes the species as Critically Endangered; while the number of individuals living in the wild is not known, catch data indicate that the population has fallen by 80 percent in the last 14 years. It is also listed in Appendix I of CITES, banning international trade.
In The Anthropologists' Cookbook (1977) Jessica Kuper noted the importance of the pa beuk to the Lao people and remarked, "In times gone by, this huge fish, which is found only in the Mekong, was fairly plentiful; but in the last few years the number taken annually has dwindled to forty, thirty or twenty, and perhaps in 1976 even fewer. This is sad, as it is a noble fish and a mysterious one, revered by the Lao."
Fishing for the Mekong giant catfish is illegal in the wild in Thailand, Laos, and Cambodia, but the bans appear to be ineffective, with the fish continuing to be caught in all three countries. However, in recognition of the threat to the species, nearly 60 Thai fishermen agreed to stop catching the endangered catfish in June 2006, to mark the 60th anniversary of Bhumibol Adulyadej's ascension to the throne of Thailand.
Thailand is the only country that allows fishing for private stocks of Giant Mekongs, this is helping to save the species as the lakes purchase the small fry from the government breeding program generating extra income that allows the breeding program to function.
Fishing lakes like Bung Sam Ran in Bangkok have this species up to 140 kg, most common size landed is 18 kg although there are some companies that specialise in landing the larger fish. These fish are non-aggressive but very powerful as they evolved in the running waters of the Mekong River where the current flow can be high at times.
The Giant Mekong can also be seen now in the Bangkok River, when feeding fish at the Bangkok temples the Giant Mekong Catfish can be seen at times the largest to date spotted has been about 25 kg.
This species needs to reach 50 – 70 kg to breed, it does not breed in lakes. The Thailand fishery Department has been running a breeding program to re-stock the Mekong River. It is yet to be seen if the fish will spawn.
Attaining an unconfirmed length of 3 m, the Mekong giant catfish grows extremely quickly, reaching a mass of 150 to 200 kg in only six years. The largest catch recorded in Thailand since record-keeping began in 1981 was a female measuring 2.7 m (roughly 9 feet) in length and weighing 293 kg (646 lb). This specimen, caught in 2005, is widely recognized as the largest freshwater fish ever caught (although sturgeon can far exceed this size, they can be anadromous). Thai Fisheries officials stripped the fish of its eggs as part of a breeding programme, intending then to release it, but the fish died in captivity and was sold as food to local villagers.