Giant Catfish in Mekong River Changes Shape – Scientists Worry

Jakarta –

A recent study found the size of giant fish in the Mekong River has shrunk alarmingly in recent years. The body length of these largest and most endangered freshwater giants, some of which are as large as grizzly bears, decreased by 40% in seven years.

Some fish, such as the Mekong giant catfish, have been studied over longer periods and show a 55% weight loss in the last 25 years. The size dropped from an average of 180 kg to 80 kg.

One of the researchers, biologist Ngor Peng Bun, once helped catch a giant catfish in 2000 weighing 270 kg, before tagging it and releasing it again. “The size is so big, it’s unforgettable,” he said and the fish almost capsized his boat.

This species, known in Khmer as trey reach or royal fish, is now only a shadow of its glory days.

The giant barb, the world’s largest carp and Cambodia’s national fish, shows a similar fate. Quoted by detikINET from the Guardian, these two species are critically endangered.

Size is a matter of survival because large fish produce far more eggs. Catfish weighing 300 kg can produce 10 to 20 times more offspring than fish weighing 50 kg. Many of the largest species are also long-lived and slow to reach maturity, meaning increasing death rates could trigger population collapse.

The Mekong giant is vital to the river’s ecosystem, but it is also central to the livelihoods of millions of people who depend on its fisheries. Scientists found a glimmer of hope when in 2022 a fisherman caught and released a record-breaking 300 kg stingray. It was the largest freshwater fish ever found and shows some giants still remain.

Fishing and hunting often target the largest animals and lead to the decline of many species, including cod in the Baltic Sea, salmon in Alaska, as well as smaller tusks on African elephants. Dr. Zeb Hogan, a professor at the University of Nevada, said the rapid decline of the Mekong giant fish was surprising.

“We see this pattern in the Atlantic cod fishery, where decades of size-based selective fishing removes the largest and most fertile fish, resulting in a dramatic collapse. As size and reproductive capacity decline, Mekong fish risk entering a ‘death spiral’. Populations survive but are no longer able to reproduce effectively,” he said.

“Knowing these giants are shrinking, both in size and numbers, is like losing a small part of Cambodia. Their existence has deep cultural and ecological significance,” said Sophorn Uy of the Royal University of Agriculture in Phnom Penh

Hogan thinks this shrinking trend is likely to continue. In addition to overfishing, the Mekong giant fish is also struggling with dams that hinder migration, the climate crisis, and the destruction of forests for agriculture, which is an important habitat.

The 300 kg stingray shows that it is not too late to act, but it is useless unless humans act now to protect this species and its river systems. “The future of the Mekong giant hangs in the balance,” Hogan said. Catching giant fish is already illegal in several countries through which the Mekong River flows, but law enforcement remains a major challenge.

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