Jeremy Hance wrote in, “Home to giant catfish and stingrays, feeding over 60 million people, and with the largest abundance of freshwater fish in the world, the Mekong River, and its numerous tributaries, brings food, culture, and life to much of Southeast Asia. Despite this, little is known about the biodiversity and ecosystems of the Mekong, which is second only to the Amazon in terms of freshwater biodiversity. Meanwhile, the river is facing an existential crisis in the form of 77 proposed dams, while population growth, pollution, and development further imperil this understudied, but vast, ecosystem. More than 850 species have been described. [Source: Jeremy Hance,, April 23, 2013 |~|]

The Mekong river is home to around 850 species of freshwater fish, many of which are only found in the region, and a host of other animals. Researchers estimate there could be over 1,200 fish species in Mekong River. Eleanor J. Sterling and Merry D. Camhi wrote in Natural History magazine, “That mesh of waterways is one of the most productive and diverse ecosystems on Earth, supporting more than 6,000 species of vertebrates alone. Its fish fauna, with some 2,000 species, of which sixty-two are endemic, exceeds all but those of the Amazon and Congo river basins. The wetlands harbor several threatened and endangered birds and mammals, including the eastern sarus crane, Grus antigone sharpii; the Bengal florican, Houbaropsis bengalensis; and the hairy-nosed otter, Lutra sumatrana, which was recently rediscovered after having been feared extinct. Sixty-five million people live there, too, 80 percent of them dependent on the river for their livelihood as farmers and fishers. [Source: Eleanor J. Sterling and Merry D. Camhi, Natural History magazine, December 2007]

“The Mekong River Basin is a microcosm of the Earth’s freshwater resources—it includes almost all of the natural forms freshwater takes on Earth: groundwater, lakes, ponds, streams, and wetlands. (Wetlands are defined as shallow, often intermittently wet habitats, such as bogs, floodplains, marshes, and swamps.) Together, freshwater ecosystems cover less than 1 percent of the Earth’s surface and hold a mere 0.008 percent of its water, but they support about 100,000 animal species—an inordinately large number for their size relative to marine and terrestrial habitats. That freshwater fauna includes a third of all known vertebrates and a whopping 40 percent of all known fish species. [Ibid]

“Their rich biodiversity aside, freshwater systems bestow untold—and underappreciated—benefits on people. Indeed, they are the very foundation of our lives and economies. The value of all the services freshwater ecosystems provide worldwide, such as drinking water, irrigation for agriculture, and climate regulation, has been estimated at $70 billion per year—a figure that assumes, rather delusionally, that one could purchase the services elsewhere if they became unavailable in nature. [Ibid]

“Species along the Mekong, as in other freshwater systems, depend on natural flood cycles for nutrients and for transportation to and from spawning grounds. More than 90 percent of the fish species in the Mekong watershed spawn not in rivers, but in seasonal lakes or periodically flooded forests and fields. [Ibid]

"Elvis" Monkey and Psychedelic Gecko Among 208 New Mekong Species Discovered

In December 2011, AP reported: “A psychedelic gecko and a monkey with an "Elvis" hairdo are among 208 new species described last year by scientists in the Mekong River region of Southeast Asia, a conservation group announced. The animals were discovered in a biodiverse region that is threatened by habitat loss, deforestation, climate change and overdevelopment, the WWF said in a report. [Source: AP, December 12, 2011]

“The newly described species include a "psychedelic gecko" in southern Vietnam and a nose-less monkey in a remote province of Myanmar that looks like it wears a pompadour. "While this species, sporting an Elvis-like hairstyle, is new to science, the local people of Myanmar know it well," the Switzerland-based group said in its report. The region is home to some of the world's most endangered species, including tigers, Asian elephants, Mekong dolphins and Mekong giant catfish, the group said.

"This is a region of extraordinary richness in terms of biodiversity but also one that is extremely fragile," said Sarah Bladen, communications director for WWF Greater Mekong. "It's losing biodiversity at a tragic rate."The Mekong flows through China, Myanmar, Laos, Thailand, Cambodia and Vietnam.In October, WWF announced Vietnam has lost its last Javan rhinoceros, making the 40 to 60 Javan rhinos living in Indonesia the last remaining members of their species.

Reuters reported: “The area's diversity is so astonishing that a new species is found every two days, but regional cooperation and decision-making must take centre stage to preserve its richness, the WWF said ched into extinction. "While the 2010 discoveries are new to science, many are already destined for the dinner table, struggling to survive in shrinking habitats and at risk of extinction," said Stuart Chapman, Conservation Director of WWF Greater Mekong, in a statement.[Source: Reuters, December 12, 2011]

Among the new species highlighted in the report "Wild Mekong" is a gecko with bright orange legs, a yellow neck, and a blue-gray body with yellow bars on its bright orange sides, discovered on an island in southern Vietnam. Then there is a black and white snub-nosed monkey whose head sports an Elvis-like hairstyle, found in Myanmar's mountainous Kachin state. Locals say the animal can be spotted with its head between its knees in rainy weather as it tries to keep rain from running into its upturned nose. Other featured creatures among the 208 new finds include a lizard that reproduces via cloning without the need for male lizards, a fish that resembles a gherkin, and five species of carnivorous pitcher plant, some of which lure in and consume rats and even birds.

"Mekong governments have to stop thinking about biodiversity protection as a cost and recognise it as an investment to ensure long-term stability," Chapman said. "The region's treasure trove of biodiversity will be lost if governments fail to invest in the conservation and maintenance of biodiversity, which is so fundamental to ensuring long-term sustainability in the face of global environmental change."

Despite restrictions, trade in wildlife remains an active threat to a range of endangered animals in the region, with some hunted because body parts -- such as rhinoceros horns -- are coveted ingredients in traditional Asian medicine. Others, such as Mekong dolphins, face threats from fishing gear such as gill nets and illegal fishing methods, prompting the WWF in August to warn that one dolphin population in the river was at high risk of extinction.

126 New Species Discovered in Greater Mekong Region in 2011

A total of 126 new species were described in Asia'a Mekong region in 2011 according to report published by the World Wildlife Fund (WWF). This was on top of 208 new species described in 2010 in the Greater Mekong region, which covers five Southeast Asia nations — Cambodia, Laos, Vietnam, Thailand, and Myanmar — as well as China's Yunnan province. [Source:, December 18, 2012]

The report issued by a group called Extra Terrestrial aims to raise public awareness of the region's high levels of biodiversity as well as threats to its native ecosystems. Extra Terrestrial tallies species described for the first time in academic publications during 2011. It counts 82 plants, 13 fish, 21 reptiles, 5 amphibians and 5 mammals. The report highlights several charismatic species, including the demonic-looking Beelzebub’s bat; a new ‘walking’ catfish from Vietnam, a minuscule (2 cm long) fish from Thailand; a blind cave fish from Laos; a frog with a bird-like call; and ruby-eyed green pit viper from Vietnam.

The report notes that 1,710 new species have been described from the Greater Mekong region since 1997. “The Mekong region has a breathtaking array of biodiversity, but many of these new species are already struggling to survive in shrinking habitats,” said Dr. Barney Long, WWF Manager of Asian Species Programs, in a statement. “It’s vital that we increase our support for protected areas and greener economic development if we want these new species protected and to ensure that other intriguing species are discovered in years to come.”

Extra Terrestrial says that large-scale dams — notably the Xayaburi dam in Laos — are a major threat to the Mekong's aquatic biodiversity. Meanwhile many species in the region are vulnerable to poaching for the wildlife trade.

The new species includes: 1) the pygmy python (Python kyaiktiyo), a 1.5m-long snake from the Kyaiktiyo wildlife sanctuary in Myanmar (Burma); 2) the blue skink (Larutia nubisilvicola); 3) aA new blind cave fish (Bangana musaei) from underground karst formations in central Laos; 4) the Quang’s tree frog (Gracixalus quangi) from Vietnam, notable for singing a different call each time it vocalizes; 5) the The Ruby-eyed pit viper (Trimeresurus rubeus), discovered in the forest of Vietnam’s Cat Tien national park; 6) The yin-yang frog (Leptobrachium leucops), one of five new amphibian species discovered in the Greater Mekong region; 7) the Beelzebub’s tube-nosed bat (Murina beelzebub) from Quang Tri province, Vietnam; and 8) the tiny Boraras naevus from southern Thailand.

Endangered Species on the Mekong River

Eleanor J. Sterling and Merry D. Camhi wrote in Natural History magazine, “As a result, even as the human population of the globe has doubled, many species that depend on freshwater ecosystems have suffered steep declines. The list would bring tears to a conservationist’s eyes: in the past three decades, a fifth of the world’s water birds, a third of freshwater mammals, a third of amphibians, and more than half of freshwater turtles and crocodiles have become either threatened, endangered, or extinct. Freshwater fishes represent a quarter of the world’s living vertebrate species, and yet more than a third are threatened or endangered. The ecology of freshwater systems may be irreversibly damaged if we humans don’t improve the way we treat them. [Source: Eleanor J. Sterling and Merry D. Camhi, Natural History magazine, December 2007]

“Fish aren’t the only victims of overexploitation. As many as 10,000 water snakes are fished from Tonle Sap Lake each day. The water snakes mainly go to feed hungry crocodiles raised for commercial export; they substitute for fish, whose populations have declined. People are fishing down the food chain in the Mekong River Basin, as in so many freshwater and marine systems. After depleting the top predators and the largest species, fishermen turn their nets on successively smaller organisms. [Ibid]

“The upshot of all those assaults is that freshwater organisms rank among the world’s most threatened species. Data on global trends are sparse, but what biologists do know paints a bleak picture of striking declines across taxa. Freshwater dragonflies, damselflies, mussels, fishes, amphibians, reptiles, birds, and mammals—all are suffering. To prevent a wave of irreversible extinctions and ecosystem collapses, people need to take better care of fragile freshwater habitats. [Ibid]

Fish in the Mekong River

Harmony Patricio, a conservation biologist and the conservation director at FISHBIO, told It has the second largest number of fish species of any river on earth, only after the Amazon River. More than 850 species have been described, and researchers estimate there could be over 1200 species. As a comparison, the whole state of California has about 67 freshwater fishes. The Mekong is also the most productive freshwater system on the planet in terms of fish biomass. The estimated annual harvest is over 2.6 million metric tonnes per year, which represents about 18 percent of the total global inland fishery harvests. That's almost 1/5 of all freshwater fish harvest across the world, found just in this one river basin. What's also special is how important the fish are for the people. There are over 60 million people that depend on the fish for protein and income, and the economic value of the fisheries is as much as $3.8 billion US dollars per year on first sale. So the river's fish are highly diverse, feed a lot of people, and are worth a lot of money. There are also some really unique and endemic species that you won't find anywhere else on earth. [Source: Jeremy Hance,, April 23, 2013 |~|]

“One obvious standout is the Mekong giant catfish (Pangasianodon gigas) because it is on record as the world's largest freshwater fish. It's like the blue whale of freshwater. It can grow to up to 3 meters long (9.8 feet), and weigh 350 kilograms (770 pounds). The giant catfish migrates long distances between several different countries, and is primarily vegetarian, which is unique for such a large fish. Another standout species would be the giant freshwater stingray, which can grow up to 2.4 meters long (7.8 feet) and 5 meters wide (16.5 feet), and weigh up to 240 kilograms (530 pounds). It's huge! |~|

“In addition to the stingray, there are other fishes you'd typically expect to find in the ocean, like electric eels and puffer fish. Some of the Pangasiid (a type of catfish) species are also really interesting. One, Pangasius krempfi, is believed to migrate to the ocean, and they have been seen along the coast of the South China Sea in Vietnam. They also migrate extensive distances, past Cambodia and over major waterfalls at the southern border of Lao, all the way up to northern Lao. The fact that they use both freshwater and saltwater and also migrate through the entire Lower Mekong Basin is pretty amazing. |~|

Giant Mekong Catfish

The Mekong giant catfish (Pangasianodon gigas) it is the world’s largest catfish fish and a candidate for the world’s largest freshwater fish. Reaching three meters (10 feet) in length and weighing almost 650 pounds (295 kilograms), its lives mainly in the lower half of the Mekong River system, in Cambodia, Laos, Thailand, and Vietnam.

According to National Geographic: Mekong giant catfish have very low-set eyes and are silvery to dark gray on top and whitish to yellow on the bottom. They are toothless herbivores who live off the plants and algae in the river. Juveniles wear the characteristic catfish “whiskers,” called barbels, but these features shrink as they age. Average life span in the wild: More than 60 years. [Source: National Geographic website]

“Highly migratory creatures, giant catfish require large stretches of river for their seasonal journeys and specific environmental conditions in their spawning and breeding areas. They are thought to rear primarily in Cambodia’s Tonle Sap lake and migrate hundreds of miles north to spawning grounds in Thailand. Dams and human encroachment, however, have severely disrupted their lifecycle. [Ibid]

Eleanor J. Sterling and Merry D. Camhi wrote in Natural History magazine, The Mekong giant catfish, is just one of the region’s struggling, overfished residents. With such grand proportions, a jackpot of succulent flesh that once sold at a premium to urban restaurants, the giant catfish was a fisherman’s prize catch. In the mid-twentieth century, hundreds of giant catfish---a naturally rare species---were caught each year, but recently the annual catch has declined to fewer than ten. Overfishing is the main cause of the decline, but habitat fragmentation and alteration of spawning grounds by dams and navigation projects also contribute. Today, the giant catfish is critically endangered, its range is greatly restricted, and the average size of individuals is declining. In recent years, Cambodia, Laos, and Thailand have outlawed catching the giant catfish. But the species is migratory, so a regional agreement may be necessary to prevent its demise. [Source: Eleanor J. Sterling and Merry D. Camhi, Natural History magazine, December 2007]

Fishermen Catch 293-Kilogram Mekong Catfish and Eat It

The largest freshwater fish ever recorded was a Mekong giant catfish caught in northern Thailand in 2005. It was nearly 2.7 meters (nine feet) long and weighed 293 kilograms (646 pounds). According to news reports: “Thai fishermen caught a 646-pound catfish believed to have been the world's largest freshwater fish ever recorded, a researcher said. The 8.9 foot long Mekong giant catfish was the heaviest recorded fish since Thailand started keeping records in 1981. The villagers had hoped to sell the fish to environmental groups, which planned to release it to spawn upriver, but it died before it could be handed over. The catfish was later sold in pieces to villagers to be eaten.”

Reporting from Hat Khrai, Thailand, Seth Mydans wrote in the International Herald Tribune, “The monster fish announced itself with four resounding whacks of its tail, thrashing against the net that had trapped it in the pale brown water of the Mekong River. It was a fish called the giant catfish and it was the size of a grizzly bear, taking five boatmen an hour to pull it in and 10 men to lift it when they reached the shore in this remote village in northern Thailand. It was only after their catch had been chopped into pieces and sold that they learned how special it was. At 2.7 meters, or 9 feet, long and weighing 293 kilograms, or 646 pounds, it may be the biggest freshwater fish ever recorded. [Source: Seth Mydans, International Herald Tribune, August 25, 2005]

“Before he headed out, one of the fishermen, Thirayuth Panthayom, made sure luck would be on his side. He said he prayed at the shrine to the God of Catfish and begged his boat to help him: "Please, Miss Boat, let me catch something today and I'll sacrifice a chicken for you." He had only been out for 15 minutes when, he said, he saw the fish smack the water four times with its tail - "Pung! Pung! Pung! Pung!" It took his crew an hour to pull it in. His father, as owner of the boat, earned nearly 80,000 baht, or about $2,000, for the fish from the village fishing association, a fortune in rural Thailand. Thirayuth, like each of the other four members of the crew, got 7,000 baht of this, which he said he gave right back to his father.

As part of its permit to fish for these endangered catfish, the village association then sold the fish to the Department of Fisheries, which harvests their eggs and sperm as part of a captive breeding program. After that, the fish are to be returned to the river. But, as usually happens, this fish, a female, did not survive the harvesting procedure, in which its belly is vigorously massaged and manipulated. In the end, the men of the village cut it into giant steaks and sold it. When he tried a bit, Thirayuth said, it tasted soft and sweet and mild. "It's hard to describe," he said. "You have to try it yourself."

Is the Mekong Catfish, the World’s Largest Freshwater Fish?

Seth Mydans wrote in the International Herald Tribune, “In one of the world's more surprising mysteries, nobody really knows which is the biggest species of fish lurking in the waters of the Mekong or the Amazon or the Yangtze or the Congo or the Colorado or Lake Baikal. When the giant catfish was caught in May 2005 [near Hat Khrai, Thailand] ,Zeb Hogan, a biologist, rushed here from an expedition in Mongolia to take a look. It was his first trophy in a project to identify and study the world's largest freshwater fish in the hope of protecting their habitats and slowing their extinction. “[Source: Seth Mydans, International Herald Tribune, August 25, 2005]

Sponsored by the National Geographic Society and the World Wildlife Fund, Hogan has embarked on an 18-month expedition that will take him to five continents and more than a dozen rivers. Some species may already be too rare to study, but he has started with the Mekong, which he said had seven species of huge fish, more than any other river, along with at least 750 other species. The Mekong giant catfish may be the first to disappear from the river, he said. The few that remain can be spotted now only in central Cambodia and here, just below the Golden Triangle, where northern Thailand, Laos and Myanmar meet.

So far, Hogan said, no one has made a credible claim to top this year's trophy. It is five times the size of the biggest catfish recorded in the United States, a 121-pound Mississippi River fish that was also caught in May. "I keep expecting people to send me photos or records of larger fish, but nobody has," he said. The candidate species must grow to at least 200 pounds or longer than 6 feet - fish like sturgeon, lungfish, gars, stingrays, carp, salmon, perch and paddlefish.

Already Hogan has a collection of unconfirmed fish stories - 3-meter catfish in Bulgaria, 500-kilogram stingrays in Southeast Asia and 5-meter arapaima in the Amazon, none of them well documented. "A lot of people say the arapaima is the largest freshwater fish, but when you look at the records, there's no reliable record of any over 200 kilograms, and certainly not over 300 kilograms," he said. Hogan has his own personal candidates, the Chinese paddlefish in the Yangtze and the giant stingray here in the Mekong.

Endangered Giant Mekong Catfish

The Mekong giant catfish is considered among the world's most threatened catfish species due to dam construction and habitat degradation along the Mekong river. The fish has been disappearing fast, from more than 60 a year caught in northern Thailand in the early 1990s to just a few today. According to National Geographic only 11 and eight fish were caught in 2001 and 2002 respectively. In 2003, fishermen captured six giant catfish in Cambodia, all of which were released as part of the Mekong Fish Conservation Project

According to National Geographic: “The world’s largest scaleless freshwater fish lives a tenuous existence in the murky brown waters of Southeast Asia’s Mekong River. Once plentiful throughout the Mekong basin, population numbers have dropped by some 95 percent over the past century, and this critically endangered behemoth now teeters on the brink of extinction. Overfishing is the primary culprit in the giant catfish’s decline, but damming of Mekong tributaries, destruction of spawning and breeding grounds, and siltation have taken a huge toll. Some experts think there may only be a few hundred adults left. [Source: National Geographic website]

International efforts are under way to save the species. Authorities in Laos and Thailand now limit total catches to four a year. In Thailand, a group of fishermen pledged to stop catching giant catfish to honor the king’s 60th year on the throne. However, enforcement of fishing restrictions in many isolated villages along the Mekong is nearly impossible, and illicit and bycatch takings continue.

Seth Mydans wrote in the International Herald Tribune, “Their decline coincides with the completion of the first of a series of dams being built upriver in southern China. Many fish cue their migrations to the rise and fall of the water, Hogan said. The giant catfish are caught in April and May when they swim upriver to spawn just north of here. [Source: Seth Mydans, International Herald Tribune, August 25, 2005]

"The damming and the blasting of rapids have changed the habitat and the river flow," Boonluen Chinarath, the village chief in Hat Khrai, told the New York Times. He had caught as many as 100 giant catfish in nearly a half-century of fishing. "The river rises and falls more quickly than before," he said. "Maybe it's up today and maybe it's down tomorrow." [Ibid]

Giant Mekong Catfish and the People of the Mekong Region

Harmony Patricio told The Mekong giant catfish has a lot of cultural importance for the local people. There is a lot of tradition surrounding how the fish is harvested in the wild. Now the wild population of giant catfish has gotten so low that most countries have made it illegal to catch a giant catfish in the river. I've talked to older fishers in villages that historically harvested the giant catfish, and it's really a sad thing for them that their children aren't going to experience that part of their culture. It was a very communal experience with a lot of ceremony involved. [Source: Jeremy Hance,, April 23, 2013 |~|]

“In some places, the whole community would get together for ceremonies and prayers. You need a lot of people to catch this fish; it's really big and heavy! After a successful harvest of a big fish, people would often share the meat and have a big ceremony and celebration. This really important cultural tradition has disappeared now.” |~|

Giant Freshwater Stingray

The giant freshwater stingray is a species of stingray native to large rivers and estuaries of Southeast Asia. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500 to 600 kilograms (1,100 to 1,300 pounds). Its numbers are dwindling due to overfishing and habitat loss, and it is in danger of extinction. The smaller freshwater whipray of New Guinea and northern Australia was once considered to be conspecific with the giant freshwater stingray but is now recognised as a separate species. [Source: Wikipedia]

Freshwater giant stingrays are among the largest of the approximately 200 species of rays. They can be found in a handful of rivers in Southeast Asia and northern Australia. The giant freshwater stingray was originally described from Thailand (where it occurs in the Chao Phraya, Nan, Mekong, Bangpakong, Prachinburi and Tapi Rivers). The giant freshwater stingray is also found in Indonesia (the Mahakam River Basin in Kalimantan) and Malaysia (the Kinabatangan River in Sabah). There are also records from various other river systems in the region. It is not clear whether all these fish are a single species or are subspecies or are a species complex. Dr Terry Bertozi, of the Evolutionary Biology Unit of the South Australian Museum in Adelaide, Australia, and is collecting genetic samples to determine whether these are the same species of stingray found in the rivers of Northern Australia.

Behavior and Characteristics of the Giant Freshwater Stingray

The giant freshwater stingray has a distinctively shaped oval disc that is widest towards the front. It is relatively thin, more or less oval-shaped pectoral fin disk and minute eyes. The snout is very broad with a projecting triangular tip. The mouth is small.The whip-like tail measures 1.8 to 2.5 times the length of the disk and lacks fin folds. The serrated spine on the tail is the largest of any stingray, reaching 38 centimeters (15 inches) long. It is covered with a sheath of toxic mucus and is capable of piercing bone. [Source: Wikipedia]

The upper surface of the body and tail are covered with small, rough tubercles, becoming sharp on the tail beyond the spine. The back is uniform brown to gray in color, sometimes becoming lighter towards the margins. The underside is white, with a distinctive broad, black band edged with small spots around the margins of the pectoral and pelvic fins. The tail is black past the spine. This species reaches at least 4.88 meters (16 feet) long and 2.13 meters (7 feet) across.

Much is still unknown about the mammoth ray species, including whether or not it can swim out to and survive at sea. The species was first described scientifically only in 1989. Its population is unknown. Many questions about it remain including: Is it truly a freshwater species? Where does it breed? What are its migratory patterns?"

The giant freshwater stingray prefers a sandy habitat. The diet of this species consists of benthic fishes and invertebrates, which it detects using electroreceptive ampullae of Lorenzini. As in other stingrays, reproduction is ovoviviparous, with females giving birth to one to two offspring at a time. A 4.3 meter (14 feet) captured female has been observed giving birth to three newborns measuring 34 centimeters (13 inches) across. Males mature at 1.37 meters (4.5 ft) across.

Endangered Giant Freshwater Stingray

The giant freshwater stingray is threatened by overfishing and habitat loss; the World Conservation Union has assessed the giant freshwater stingray as endangered over most of its range, except in Thailand where it is Critically Endangered. It is occasionally caught as bycatch by longlines and gillnets in central Thailand and likely elsewhere. This species is sold for meat and possibly cartilage; adult fish are not usually used for food but may still be killed or maimed by fishers. There is a growing sport fishery for this species. When caught on a line, it may bury itself under large quantities of mud, making it almost impossible to lift. It is also capable of pulling boats significant distances or underwater.

In Thailand, the freshwater stingray is assessed as Critically Endangered with a high risk of extinction. A combination of deforestation, dam construction, and development has degraded, altered, and fragmented river habitats such as that only a fraction of Thailand's native fish species still breed in the wild. In the 1990s, the Thai government initiated a captive breeding program to bolster the population of this and other freshwater stingray species until the habitat degradation can be remedied. However, the program was later put "on hold".

Search for the Giant Freshwater Stingray: the World’s Largest Freshwater Fish?

Michael Casey of Associated Press wrote: “American biologist Zeb Hogan is on a worldwide quest for the largest freshwater fish. He has heard the stories of Cambodian fishermen catching rays that weighed more than 1,100 pounds with wingspans of 14 feet. But so far they are just stories. If he can confirm them, his find could eclipse the world record now held by the Mekong giant catfish: a 646-pound specimen caught in 2005 in Thailand. "It could be the largest fish in the world and we know next to nothing about it," Hogan says. "I've spent five years on the Mekong looking for rays and only saw two or three. They were nowhere near the size I'd heard about." [Source: Michael Casey, Associated Press, July 20, 2008 /=\]

Hogan's quest is part of the Megafishes Project financed by the National Geographic Society. The three-year project, which started in 2006, aims to document and protect freshwater giants that weigh at least 200 pounds or measure at least 6 feet long. It will take Hogan to 14 freshwater systems on six continents, including the Mekong, Nile, Mississippi and Amazon rivers. Time is running out for many of the species. The Chinese paddlefish and the dog-eating catfish in Southeast Asia are on the brink of extinction because of pollution, overfishing and dam building. In the Yangtze, where the Three Gorges Dam is a serious threat, Chinese paddlefish haven't been caught since 2003. "Of the two dozen or so species of giant fish, about 70 percent are threatened with extinction," says Hogan, an assistant research professor at the University of Nevada, Reno.

Hogan dresses like a tourist, with a baseball cap and shorts, and has the boyish enthusiasm of an explorer. He spends much of the year searching for these large fish. He has focused mostly on Asia, where he once traveled 36 hours by road to catch the taimen in Mongolia. He just returned from Bhutan, where he scoured river canyons for mahseer. Hogan said he was drawn to the freshwater ray, known scientifically as Himantura chaophraya, because so little is known about it.

Hogan spent the last few years on the Mekong in a futile effort to catch rays because the nets of Cambodian fishermen were no match for them. Rays also are nearly impossible to spot because they spend much of their time scrounging for small fish, shrimp, crabs and mollusks that live on the bottom of muddy rivers. Hogan got wind of big rays being caught and released by Rick Humphreys' company FishSiam in Thailand. Unlike the Cambodian fishermen, FishSiam uses modern rods and reels used to catch other big game fish. At first he was skeptical, then excited.

Catching a Small Giant Freshwater Stingray

Reporting from Samut Songkram, Thailand, Michael Casey of Associated Press wrote: “Rushing across a temple parking lot, British angler Rick Humphreys yells, "We've got a fish." He jumps into a small motorboat on the Mae Klong River in time to see Wirat Moungnum bring the prize to the surface: a rare giant freshwater stingray that weighs as much as 44 pounds. It bursts through the murky water exposing a soft, white underbelly the size of a trash can lid. The crew scrambles to string a rope through its gill-like slits and wrap a towel around its 5-foot-long tail, which has a venomous barb. "It's a start," Humphreys says almost apologetically. The specimen is a tenth the size of the largest rays. "There are a lot bigger ones than that." [Source: Michael Casey, Associated Press, July 20, 2008 /=\]

Humphreys seems an unlikely partner in Hogan's quest. He has no scientific training. But he knows how to fish, and his team's success in catching stingrays is almost unmatched in Thailand. Just in the last year, Humphreys and his partner, Wuttichai Khuensuwan, have caught 40 rays on the Bang Pakong and Mae Klong Rivers, with the largest weighing in at 485 pounds. Humphreys, who got his start catching carp in West London gravel pits, says he prefers stingrays because of their fight. They routinely break fishing lines, he says, and one took 15 of his men about six hours to bring to the surface. "Their strength is legendary," he says. "When you see them in the flesh, it is quite humbling."

Catching a ray can be dangerous, he says, especially before its tail has been neutralized. Wuttichai Kuachareonsri, a member of Humphreys' crew, stopped fishing for a year after he was stung in the leg. "I never have felt pain like that," he says. "It really frightened me." On his fishing trip with Hogan, Humphreys boasts about "monsters" below the tranquil river and insists that it is a matter of time before his team lands a world record ray.

The anglers head to the Bang Pakong and Mae Klong rivers just a two hours' drive outside Bangkok, winding their way past office towers, Buddhist temples and busy highways. Fish farming pens dot the riverbanks, and sounds of construction and puttering boats echo across the water. Both spots have given up rays in the past. But on the their first day on the Bang Pakong, the fishermen come up empty. Humphreys blames the heavy rains that have swollen the river. The next day, they have better luck on the Mae Klong.

The rod bends almost into the water, and Wirat struggles for almost half an hour as the ray dives under the boat and across the bow. It finally is brought to the surface, revealing its big bulging eyes and dark, coarse skin. Its tail alone is 12 feet long. Hogan says catching such a big ray so close to a big city is a sign the species is thriving despite pollution. He is awaiting government permission to launch a two-year study to catch and tag 20 to 30 more rays to better understand their movements.

Giant Freshwater Stingray Caught by Fishermen

In February 2008, reported: “One of our readers has sent in this photo of an enormous and rare giant freshwater stingray caught in December 2007. The monster ray was caught in the Ban Pakong River 80 kms east of Bangkok. The fish was captured by Tom Parker from Coventry whilst fishing on a guided freshwater angling expedition. The immense size of the fish made it impossible to weigh. With a wingspan of 2.4m the giant ray was estimated to weigh in the region of 170 to 200 kilograms. [Source:, February 2008]

The capture was made in the lower tidal reaches near Chachoengsao and took almost an hour to land. The fish was released after capture.Amazingly, 12 different specimens of this species have been caught in the last three to four months from two different rivers, the Ban Pakong and Maeklong Rivers. One of these captures may well have been a newborn of just 12 centimeters in size caught from the Maeklong River. This is a good sign for this river which has been affected by pollution in previous years and also a good sign for this elusive and nomadic species.

In February 2009, reported: “A giant freshwater stingray was caught in the Maeklong River in Thailand in January 2009, weighing as much as 350 kilograms, by Dr. Ian Welch, a freshwater biologist, who had been visiting Thailand in conjunction with the National Geographic Society to help with a stingray tagging programme. Dr Welch and the Fishsiam team, who are also helping with the research, landed this extraordinary fish on whilst filming a documentary with the Dr. Zeb Hogan and the National Geographic Society about "Megafishes". The fish was estimated by scientists present at the capture to weigh an extraordinary 265+ kilograms. The fish was observed to be pregnant and was released soon after capture.The expedition also involved a research project given official approval by the Thai authorities to tag Giant freshwater stingray and monitor stingray populations in both the Ban Pakong and Maeklong Rivers.

Zeb Hogan told the New York Times, "I saw a stingray in Cambodia in 2003 that was 4.13 meters long. It had a disc 2 meters across and 2 meters long, and the tail was 2.13 meters long. That fish could have been it, but we couldn't weigh it. It was too big." When he began to spread the word in Cambodia that he was looking for giant fish, Hogan said, it was stingray he had in mind. "I thought I'd get 50 phone calls the first week, but nobody contacted us," he said. "So they're more rare than I thought they were."

Candidate for the World’s Largest Freshwater Fish

In February 2009, National Geographic reported: “Fishers and scientists announced the catch, and release, of what is likely the world's largest known freshwater giant stingray. The giant stingray, weighing an estimated 550 to 990 pounds (250 to 450 kilograms) was reeled in on January 28, 2009, as part of a National Geographic expedition in Thailand. The stingray's body measured 6.6 feet (2 meters) wide by 6.9 feet (2.1) meters long. The tail was missing. If it had been there, the ray's total length would have been between 14.8 and 16.4 feet (4.5 and 5 meters), estimated University of Nevada Biologist Zeb Hogan. Hogan was in Thailand searching for giant fish as part of the Megafishes Project. [Source: National Geographic, February 24, 2009]

The new find gives Hogan hope that the giant stingray, once overfished, may be more abundant than previously thought. And it may confirm the giant stingray as the heavyweight champ of the Megafishes Project. "Honestly, we just don't know how much it weighed. But it's clear that the giant stingray has the potential to be the largest freshwater fish in the world," said Hogan. "The Thai populations were once considered critically endangered, although with the discovery of new populations the stingray's abundance appears higher than previously believed," added Hogan. The International Union for Conservation of Nature (IUCN) currently lists the freshwater giant stingray as vulnerable. In March 2008, Hogan found a 14-foot-long (4.3-meter-long) ray near the Thai city of Chachoengsao.

Mekong River Irrawaddy Dolphin

There are a few dozen freshwater dolphin---the Irrawaddy dolphin—living in the Mekong River. Harmony Patricio told The dolphin that has a lot of cultural significance.“People really honor the dolphin, and there are many stories about dolphins helping drowning people or helping fishermen to catch fish. So they never kill the dolphins.

T he Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190 kilometers stretch of the Mekong River between Cambodia and Laos. The latest population is estimated between 64 and 76 members (2008 figures). The Irrawaddy dolphin is identified by a bulging forehead, a short beak, and 12-19 teeth on each side of each jaw. The pectoral fin is broadly triangular. There is a small dorsal fin, on the posterior end of the back.

In 2004, the Irrawaddy dolphin was declared a protected species. Most are found around the Khone Falls area in the Mekong River along the Laos-Cambodia border. Some believe they will be extinct in less than 50 years. Many have been killed by gill nets and dynamite fishing used mostly by Cambodians. Some fishermen have purposely caught them for their teeth, which are regarded as talismans against evil spirits Today villagers are encouraged to participate in the tourism trade in the area and so they have reason to conserve the dolphins.

Khon Island near Siphandan (on the Mekong River north of the Cambodian border) is place where tourist gather to try and catch a glimpse of the river dolphins. They are most likely to be seen off the southern tip of the island in the early morning or late afternoon from December to May. The best spot of all is on Kham Island, a small sand island within Cambodian territory on the Mekong River. Boats make runs to this island for a small fee. Viewing the dolphins from boats isn’t really practical because the boats scare the dolphins off.

See Asian River Dolphins

Irrawaddy Dolphins in Cambodia

The Irrawaddy dolphins found in Cambodia live mainly in the Mekong River around Kratie and Stung Treng provinces. The number of these mammals is estimated to be between 40 and 60 and they are often seen travelling in small groups of 6 to 10 individuals. The females usually give birth to young once every two years most often during the months of June to August. The young dolphins are about 1 meter in length at birth and suckle milk. By adulthood the dolphins can attain a length of over 2.5 meters and weigh up to 180 kilograms. Their diet consists mainly of small fish, shellfish and snails. The dolphins can swim at speeds up to 40 kilometers per hour and stay submerged for periods between five and ten minutes.

The Dolphin Habitat in Kratie, Cambodia is situated at Kampee Village and Resort in the Sambok Commune. Besides being a wonderful tourist hub the Dolphin Habitat, also plays a significant role in the conservation of dolphins. The Irrawaddy Dolphins make their home on a beautiful stretch of the Mekong River near a small set of rapids. They make upward arches, breaking the surface of the water as they swim about the area. The dolphins are most active in the early morning hours (around 6 am) and the late afternoon and early evening hours. A local family hires out their small boat. A young man in the family takes you out on the river for a closer look. The charge is 3,500 riel per person.

The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190 kilometers stretch of the Mekong River between Cambodia and Laos. The latest population is estimated between 64 and 76 members (2008 figures). The Irrawaddy dolphin is identified by a bulging forehead, a short beak, and 12-19 teeth on each side of each jaw. The pectoral fin is broadly triangular. There is a small dorsal fin, on the posterior end of the back.

Mekong Dolphin near Extinction, WWF Says

In June 2009. AFP reported: “Pollution in Southeast Asia’s Mekong River has pushed freshwater dolphins in Cambodia and Laos to the brink of extinction, an international conservation group said. The World Wide Fund For Nature (WWF) said only 64 to 76 Irrawaddy dolphins remain in the Mekong after toxic levels of pesticides, mercury and other pollutants were found in more than 50 calves who have died since 2003. “These pollutants are widely distributed in the environment and so the source of this pollution may involve several countries through which the Mekong River flows,” WWF veterinary surgeon Verne Dove said in a press statement. [Source: AFP, June 19, 2009]

The organization said it was investigating how environmental contaminants got into the Mekong, which flows through Cambodia, Laos, Myanmar, Thailand, Vietnam and the southern Chinese province of Yunnan. The WWF said it suspected that high levels of mercury found in some dead dolphins came from gold mining activities. It added that Irrawaddy dolphins in Cambodia and Laos urgently needed a health program to counter the effects of pollution on their immune systems.

Inbreeding among the small population could have also contributed to weakened immune systems of the young dead dolphins, all of whom were under two weeks old. “The Mekong River dolphins are isolated from other members of their species and they need our help,” WWF Cambodia country director Seng Teak said, adding that the mammals “can show remarkable resilience” if their habitat is protected.

The Mekong River Irrawaddy dolphin, which inhabits a 190km stretch in Cambodia and Laos, has been listed as critically endangered since 2004, the WWF said. Thousands of Irrawaddy dolphins once swam in the Mekong. Although regarded as sacred in Cambodia and Laos, their numbers were cut by illegal fishing nets and Cambodia’s drawn-out civil conflict, in which dolphin blubber was used to lubricate machine parts and fuel lamps.

The Mekong is one of only five freshwater habitats in the world for the Irrawaddy dolphin, and Cambodia was thought to support its largest remaining population. With their pale grey skin and blunt beaks, Irrawaddy dolphins resemble porpoises more than their sea-going cousins, and congregate in a handful of the Mekong’s natural deep-water pools.

The Cambodian government has been promoting dolphin-watching to attract ecotourism and cracked down on the use of illegal nets that entangled them. It was hoped that banning fishing nets in dolphins’ protected areas would raise their number to 170 within the next few years.

Threats to Fish and Wildlife in the Mekong River

Jeremy Hance of wrote: “One of the most immediate threats, however, is the proposed construction of 77 dams on the river, including the controversial Xayaburi Dam, which Patricio says could interrupt the migration of the giant catfish. Considered the world's biggest freshwater fish, the giant catfish is listed as Critically Endangered and has largely vanished in recent decades. Despite it's incredible size, scientists still know little about the animal. [Source: Jeremy Hance,, April 23, 2013 |~|]

"Overall, the cumulative effect [of dam construction] will probably be a reduction in the number of migratory species and a shift in the species composition to favor species that do well in reservoirs," says Patricio. "Right now, we know more than a third (38 percent) of the total Mekong fish harvest consists of migratory species. If the biomass of the reservoir species doesn't scale up to replace the migratory species, we could see a decline in total harvest or productivity." |~|

Conservation on the Mekong River

Jeremy Hance of wrote: “A new program by FISHBIO, headed by Patricio, is working to compile and disperse data on the freshwater fish across the region, including gathering information on harvesting. The Mekong Fish Network, as it's called, hopes to draft baseline data, so that information can be compared over regions and time.FISHBIO is a fisheries and environmental consulting company with offices in Chico and Oakdale, California, and Vientiane, Laos. The group is dedicated to advancing the research, monitoring, and conservation of fishes around the world. To support global conservation efforts, FISHBIO partners with international agencies, NGOs, and local communities to provide technical assistance and share expertise developed through years of experience with freshwater fish monitoring in California. FISHBIO has provided funding and resources for a number of conservation projects in the Mekong region, reflecting the company's mission to improve the study and sustainable management of fishes. [Source: Jeremy Hance,, April 23, 2013 |~|]

Patricio said:“The main goal of the Mekong Fish Network is to help people working with fish in the different countries of the Mekong Basin to collaborate across national borders and share information so we can better understand what's happening with Mekong fishes throughout the basin. These fish migrate between six different countries: China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam. These countries all speak different languages and have different cultures and government structures, but the fish don't abide by national borders. They use different parts of the river basin for different parts of their life cycle, so sustainably managing or conserving these fishes requires international cooperation." |~|

“Conservation has been a challenge since there is so much we don't know about the basic biology, life cycles, and ecology of the fishes. There needs to be more funding and more technical expertise made available to the region so this basic species information can be used to design conservation strategies. In a multinational region with migratory fish, conservation also has to work across borders. The fish move between different countries, so you really need the countries to agree to work together and conserve the fish at all the different stages of their life cycles. |~|

Research on the Mekong River

Patricio told “We also hope to develop and implement standardized fish sampling methods throughout the basin to build a long-term monitoring program that studies how these fish populations change over time. No basin-wide program like this currently exists, and we need it if we want to achieve more sustainable fisheries management, conserve some of these rare or migratory species that are on the brink of extinction, and sustain the river's productivity that people rely on for food and income. |~|

“FISHBIO worked with the U.S. Geological Survey to convene a consultation workshop in Cambodia in 2012, which brought together fish researchers and mangers from across the basin to talk about pressing issues and what tools they need to better study and manage Mekong fish. The Mekong Fish Network was designed in response to their requests to provide tools and resources that can help build technical capacity and advance scientific study across borders. |~|

“A lot of good research has been done in the region, but part of the challenge is sharing that research and information across institutions and national borders. You either have to translate everything, or everybody has to learn one language. The river also covers a huge geographic area that is incredibly diverse, both culturally and ecologically. The habitat changes dramatically from northern Laos to Cambodia to the Mekong Delta in Vietnam. The river in northern Laos is bounded by high mountains with deep, rocky gorges. In southern Laos there are huge waterfalls, and in Cambodia the river spreads out, gets more sandy and flat. Cambodia's great lake, the Tonle Sap, is like a huge flood plain of fish rearing habitat. A lot of the delta is very developed, with many different channels. It's challenging to conduct research in such a wide variety of habitat types. |~|

“There is also a real need to build technical capacity for research and conservation among local agencies and researchers, particularly in Laos and Cambodia. Even something really fundamental like data management is a challenge. People may not have trained IT staff or the skills to build a database, maybe they can't afford to buy licensed software, their data could get corrupted, or it never gets analyzed if project funding ends. To address some of these issues, FISHBIO has worked with the U.S. Geological Survey to develop the Mekong Fish Network Data Bank, which is a free tool to help Mekong researchers store, manage, and share their data. ( |~|

“We want to improve fish distribution data and identify important spawning locations and migration periods. We also want to improve fish population estimates. Right now, all the population estimates are based on catch statistics, which I think is a good proxy, but it doesn't tell you about the fish that people aren't catching. For example, the giant stingray is very rarely caught, and isn't targeted at all for fishing. People currently aren't going out there trying to figure out where the giant stingray spawns, how much habitat it needs, where it eats, how much it moves around. So we want to improve our knowledge of fish that aren't targets for harvest. |~|

“One of the main things we want to do is track trends over time and see what happens to fish populations as we see changes in harvest pressure and environmental conditions. The first thing we need to know if we want to manage fisheries is if the populations are going up or down. Developing a set of standard data that we collect across the basin will allow us to compare fish data between locations and over time —that's a really important goal of the Mekong Fish Network. |~|

Impact of Dams on Mekong River Fish Species

Harmony Patricio told “The strategic environmental assessment for mainstem dams that was commissioned by the Mekong River Commission suggests that mainstem dams like the Xayaburi could block the migrations of some rare or economically valuable species. It could alter the species composition to favor fish species better adapted to a reservoir environment. The fish that can withstand lower oxygen levels or higher temperatures and can survive in a reservoir will do better than fish that need the free-flowing river environment or that are highly migratory. [Source: Jeremy Hance,, April 23, 2013 |~|]

“Also, no one knows for sure where the giant catfish spawns, but based on local ecological knowledge, people believe they spawn upstream of the Xayaburi Dam location. It would be a problem if the giant catfish can't make it past the dam, but they've already stopped showing up to these traditional spawning grounds—they've already been affected by changes to the river. Maybe they will be able to spawn somewhere downstream of the dam. The dam could also trap sediment that is very important for maintaining downstream habitat in the Mekong Delta in Vietnam. Ultimately, the Xayaburi is likely to have some impacts on fish, but there are plans for many other dams as well. |~|

“The impact is really going to depend on the development scenario: whether all of those dams are built in the locations where they're planned now, and how they're built. There are many alternative scenarios that could reduce impacts on fish and still generate a substantial amount of electricity. Overall, the cumulative effect will probably be a reduction in the number of migratory species and a shift in the species composition to favor species that do well in reservoirs. Right now, we know more than a third (38 percent) of the total Mekong fish harvest consists of migratory species. If the biomass of the reservoir species doesn't scale up to replace the migratory species, we could see a decline in total harvest or productivity. |~|

“The sediment trapping could reduce the productivity of the marine fishery off the coast of the delta and the delta itself could suffer land loss from erosion, which might affect rice production. People also talk about how dams will change the river's flow regime. Right now the Mekong has a very dynamic regime, extremely high flows in the rainy season, and very low flows in the dry season. This difference in flows is one reason why people think the river so productive. It causes the flooding of the Tonle Sap, creates floodplain habitat, and the potential for riverside gardens. A lot reservoirs and dams will reduce the variability of the flow regime. The dry season flows will be higher and the wet season flows might be a bit lower. There are a lot of questions about how this will affect the system. |~|

Mitigating the Impact of the Mekong River Dams on Fish

Jeremy Hance of wrote: “There are ways to mitigate the damage of the dams, such as building massive bypass channels around the dam. In addition, officials could look at other power-generation technologies that wouldn't involve damming the river.[Source: Jeremy Hance,, April 23, 2013 |~|]

Patricio told Mongabay: “There are definitely ways to design dams to minimize their impacts on fish. You might have to sacrifice a bit of the power generation capacity, but maybe it will be worth the gain you get from maintaining fish populations. One strategy they're looking at now for dams on the Mekong mainstem is building big bypass channels, basically creating a new river channel that goes around the dam. It's obviously not as big and wide as the natural river, but it provides fish with a more natural riverine environment, rather than trying to build an elaborate fish ladder or elevator system over the dam itself. I think that approach is probably the most "fish-friendly." |~|

“It depends on what kind of fish you're talking about! Fish passage is a challenge because there are more than 100 highly migratory fish species in the Mekong, ranging in size from less than 10 centimeters up to 300 centimeters. Obviously, their swimming and jumping capabilities are going to be really different. In addition, huge volumes of fish move at the same time in the Mekong, and it's hard to engineer something that can accommodate such a huge quantity of fish to pass a dam. |~|

“There are also ways of generating hydropower without making big dams. Some cool research is looking into building small turbines that are bolted to the riverbed, like free-standing barrels. Screens protect the fish from the turbines, and there is lots of space for fish to pass around. People are also designing mesh grids with tiny turbines, maybe the size of a cube of ice. You put that on the substrate, and the little turbines combine to produce a fair amount of electricity, although they can't generate the amount of electricity that the large dams can. I would say the most fish-friendly approach would be to use these small-scale, alternative technologies that maybe can't produce as much power per facility, but you could spread lots of them out in places that aren't essential for spawning or feeding. |~|

Image Sources: Wikimedia Commons

Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Global Viewpoint (Christian Science Monitor), Foreign Policy, Wikipedia, BBC, CNN, NBC News, Fox News and various books and other publications.

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© 2008 Jeffrey Hays

Last updated April 2014

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