The Mekong, twelfth longest river in the world, is the habitat of some of the world's
largest freshwater fish: the giant catfish, giant carp, and giant stingray.
This giant carp, caught in the Tonle Sap in December 2002, measured 1.72 meters long and weighed 102 kilograms.
They are not popular eating fish, but their numbers have declined due to accidental
Cambodia remains one of the last strongholds of the giant fish. This is in part due
to the unique annual cycle of flooding and draining between the Tonle Sap lake and
the Mekong, which is responsible for Cambodia's huge fish resources. There are at
least 1200 species of fish in the Mekong Basin and only 10 to 20 percent of them
form the basis of the fisheries trade.
Cambodians are not surprised by stories of giant fish in the Mekong; for centuries
the Naga, a serpent that dwells in the river, has been an integral part of their
Environmental threats to the Mekong have focused new attention on aquatic biodiversity.
"Conservation in Cambodia is almost entirely terrestrial," says Zeb Hogan,
an American fish conservationist who is working with the National Geographic Society
to learn more about the giant fish of the Mekong. "We need to see what is in
the rivers in order to protect them."
The giant catfish (Pangasianodon gigas) is still regularly caught two kilometers
north of the Japanese Friendship Bridge in Phnom Penh, where the main river channel
is narrow and a prime spot for nets.
Fish in their thousands, but tiddlers compared with the Mekong's giants.
The giant catfish can weigh as much as 300 kilograms and may be up to three meters
long. The main season these leviathans are caught is between October and December.
The giant catfish is not considered good eating but has acquired a god-like status
(Khmers call it trey reach, the royal fish). It is believed the fish uses either
lunar or tidal forces to navigate to its spawning grounds, passing through Phnom
Penh on its way.
Between October and March, when the migratory fish species leave the Tonle Sap and
swim into the Mekong and upstream, bagnet fisheries are established in the Tonle
Sap. They consist of two to six nets spread across the river. Each net can be 100
to 120 meters long with a 25-meter-wide entrance.
The conservation of the giant species is seen as a microcosm of aquatic conservation
in Cambodia: if such large animals cannot be protected then there is little hope
for smaller creatures. Nao Thuok, Deputy Director of Fisheries at the Ministry of
Agriculture, Forestry and Fisheries, says, "As the largest fish in the Mekong,
conservation of the catfish is important as an example for all fish."
"The catfish and giant carp (Catlocarpio siamensis) symbolize the ecological
integrity of the Mekong River," says Hogan. "The catfish migrates out of
the Tonle Sap and into the mainstream Mekong in the rainy season; this is common
with most Cambodian Mekong fish and as such the protection of this migratory pathway
benefits a huge array of fish.
Zeb Hogan tags a Mekong fish.
The catfish is no longer caught in other countries through which the Mekong passes.
Hogan says between five and ten are caught annually in Cambodia. He estimates that
the population in the Mekong basin has decreased over the last 50 years by 90 percent.
"The giant catfish is one of the most vulnerable species in the Mekong River
basin," says Hogan.
The giant catfish was registered as critically endangered by the World Conservation
Union this year in 2003.
To raise awareness about the fish's plight a local wildlife NGO, Save Cambodia's
Wildlife, Sang Kros Satprey, recently released a book entitled Samnang and the Giant
Little hard research has been done on some of the other larger fish. "The lack
of research is what is hampering our conservation efforts," Thuok says.
Hogan hopes this will change: "For the 2004 project we hope to include the freshwater
stingray and other giant fish species such as the freshwater sawfish, freshwater
sharks and the infamous dog-eating catfish." Since 2000 Hogan has been running
a buy-and-release research project for the giant catfish that includes a tagging
program that is providing insights into the migratory habits of the fish.
This giant stingray was caught in the Mekong in Prey Veng province in December 2002. Measuring 4.2 metres by 2 metres, it was too heavy to weigh, but was tagged and released. "It's the largest fish I've ever seen in the Mekong," says Zeb Hogan of the National Geographic Society.
The giant stingray (Himantura chaopraya) was only discovered in 1987. Considering
its four-meter-by-two-meter size it seems odd that it was not discovered earlier.
Its preference for deep parts of the river is thought to be the reason it has existed
for so long without scientific discovery. Freshwater stingrays inhabit other big
rivers, including the Orinoco and the Amazon.
The depth of the river is thought to be the key to the survival of large fish in
conjunction with a diverse and complex basin of tributaries. "The survival of
these species is the richness of the food in association with the deep pools,"
Samnang and the Giant Catfish states that "the deep pools of the Mekong, some
of which may be over 60 meters in depth, are important dry-season habitat for fish.
Fishermen report that at least 53 fish species live in deep pools."
In Kratie and Steung Treng provinces, in the Mekong 58 deep pools have been identified
in a MRC report. Thouk says the total has now increased to 97 deep pools, the deepest
being 80 meters. They serve as a dry season refuge for fish, especially the larger
ones. But even these pools are vulnerable to human impact.
There are projects under way to blast the river's reefs for commercial navigation
as agreed in the Commercial Navigation Treaty between Laos, China, Burma and Thailand.
As the Phnom Penh Post reported last year, neither Vietnam, nor Cambodia was consulted
about the agreement. Such blasting could affect the flow of the river and thus these
crucial deep pools. Such a change in flow could disrupt the migratory patterns of
the fish because they are adapted to seasonality.
Hydro-electric dams would also have a large impact on the aquatic biodiversity. Prime
Minister Hun Sen in a speech to the Second International Symposium on the Management
of Large Rivers for Fisheries, in February 2003, speculated on the possible impacts
the commercial navigation plan and damming would have on Cambodia: "The Tonle
Sap could dry up; ending the famous river fishing industry and causing widespread
flooding, and eventually the home of endangered fish would be destroyed."
The largest scaleless freshwater fish in the world: a giant catfish caught, tagged and released on October 21, 2002, in the Tonle Sap.
Local examples of the ecological impact of dams indicate some ominous trends. A Mekong
River Commission report on the impact of the Yali dam on the Sesan River in Ratanakkiri,
a tributary of the Mekong, says that due to increased silt the deep pools are shrinking.
One specific case study shows that in Voeun Say district within the last three years
one pool that was between seven and eight meters deep has shrunk to less than one
"There is no emphasis on the aquatic conservation of the Mekong," Hogan
The river has been seen more as a commodity producer than a habitat by the countries
involved in its development and management. Its source was only discovered in 1995
in the snowy plateaus of Tibet, one year after the first bridge was completed.
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