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Asian Catfish Migrates Hundreds of Miles, Rivals Salmon
Stefan Lovgren
for National Geographic News
September 7, 2007
http://news.nationalgeographic.com/news/2007/09/070907-catfish-migrate.html
Despite their reputation as pond-dwelling scum suckers, some catfish
may be as well traveled as salmon.
A new study shows that a species of Southeast Asian catfish, Pangasius
krempfi, is anadromous, meaning that it moves from coastal waters into
fresh waters to spawn.
Each year the species travels more than 600 miles (1,000 kilometers)
from the South China Sea up the Mekong River (see a map of the
region).
"This is similar to many salmon species that spend the first part of
their lives at sea and then migrate hundreds-or even thousands-of
miles up coastal rivers to spawn," said Zeb Hogan, a fisheries
biologist with the University of Nevada in Reno.
Hogan is a co-author of the new study, which appears in this month's
issue of the Journal of Fish Biology.
Heok Hee Ng, a fish biologist at the National University of Singapore
who was not involved in the study, said that the findings show that
catfish are not "inactive dullards" after all.
"It certainly should change the way the general public looks at
catfish," he said.
The new findings also suggest that related catfish species all over
the world may be more migratory than previously thought.
Conservationists warn that a proposed hydroelectric dam on the Mekong
in Laos could have a devastating impact on the river's many catfish
species.
"There is clear evidence that Hou Sahong-the proposed site for the
Khone Falls dam-is a major corridor for migratory fish and one of the
worst possible locations in the entire basin to build a dam," Hogan
said.
Connecting the Dots
Catfish are named for their prominent barbels, organs near their
mouths that resemble a cat's whiskers. Thousands of catfish species
swim Earth's rivers and streams, including some of the largest and
smallest freshwater fish on the planet.
Study co-author Hogan heads the National Geographic Society's
Megafishes Project, a three-year program launched this year that will
document the world's largest freshwater fishes.
(National Geographic News is part of the National Geographic Society.)
Many catfish species are believed to be migratory, Hogan noted, but
they live in murky rivers, making documentation of their movements
difficult.
"We did suspect that Pangasius krempfi was anadromous, because
fishermen reported the species in the South China Sea and far up the
Mekong," Hogan said.
"The challenge was to connect the dots-to show that the fish from the
South China Sea and the Mekong were part of the same population."
The scientists examined chemical markers called isotopes in bone and
muscle tissue of catfish from the Khone Falls region of the Mekong.
The team found evidence that the freshwater-dwelling fish had migrated
recently from a marine habitat.
John Lundberg is curator of fish in the department of ichthyology at
the Academy of Natural Sciences in Philadelphia, Pennsylvania.
"As far as I know ... this is the first record of a riverine catfish
migration between marine and freshwater habitats based on radioisotope
evidence," Lundberg said via email.
"This is a highly regarded method, so I would say the finding is
sound. ... [O]ne hopes now that catch data will confirm the presence of
Pangasius krempfi in seawater."
National University of Singapore's Ng added: "The fact that these
large catfishes have been fished for hundreds of years, and yet it is
only recently that we know that these are anadromous, shows how little
we know about the biology of many of these catfish species."
Famous Soup
P. krempfi is closely related to more than ten other species of Asian
catfish.
Its relatives include the Mekong giant catfish and the Chao Phraya
giant catfish-often called the "dog-eating" catfish because of its
taste for canine carcasses.
A Mekong giant catfish caught in 2005 measured about 9 feet (2.7
meters) long and weighed 646 pounds (293 kilograms).
P. krempfi grows up to 4 feet (1.2 meters) long, and the species is a
popular food. In Vietnam-one of six countries the Mekong passes through
-the fish is the main ingredient in a famous soup.
But news that the species is migratory could have serious implications
for its conservation, experts warn.
Scientists point out that migratory fish are more vulnerable to
extinction, because they fish rely on a variety of habitats to
complete their life cycles.
Fishers can also easily target such species during spawning runs.
The new study suggests that the fish's ability to spawn might be
compromised by the plans to build a dam at Khone Falls.
More than 98 percent of the P. krempfi caught each year in the Khone
Falls region are taken between mid-May and June, the research shows.
This leads scientists to believe that the catfish swim through the
area only once a year, probably during spawning.
Study co-author Hogan said that "plans for a dam on the mainstream
Mekong threaten migratory fish, which in turn threatens the
livelihoods of the millions of people in the Mekong that depend on
fish for food."
Ian Baird, a study co-author at the University of British Columbia in
Vancouver, said that the study highlights the need for all six
countries that contain the Mekong to cooperate on protecting the river
and its wildlife.
"Fish species do not recognize socially constructed national borders,"
he said.
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