Is it the end for the Mekong giant catfish?

(Photo: Jean-Francois Helias)

Thursday 12 August 2010
Dr Heok Hee Ng
Practical Fishkeeping (UK)

Proposed dams in the lower Mekong River in the Indochinese peninsula will doom the Mekong giant catfish (Pangasianodon gigas) to extinction, according to the report “River of Giants: Giant Fish of the Mekong” recently released by the World Wildlife Fund.

There are 11 dams proposed in the Mekong River south of China (eight in Laos and three in Cambodia), and the construction of any one of these dams will prevent the catfish from migrating upriver (from the Tonle Sap Lake in Cambodia to northern Thailand and Laos) to spawn.

The catfish, reaching sizes of up to 3m and weights of up to 350 kg, cannot swim across dams because of their sheer bulk, making fish ladders (the traditional solution in allowing migratory fish to pass through artificial barriers such as dams) useless in alleviating this problem.

Populations of the giant Mekong catfish have already plummeted by 90% over two decades, and the dams might prove to be the last straw.

The dams not only spell doom for the Mekong giant catfish, as the Mekong River is also home to four of the world's 10 largest freshwater fish species.

The other three species, also highlighted in the report, are the giant freshwater stingray (Himantura chaophraya) pictured above, the giant dog-eating catfish (Pangasius sanitwongsei), and the giant barb (Catlocarpio siamensis).

According to Dang Thuy Trang, Mekong River Ecoregion Coordinator for the WWF Greater Mekong Programme, "More giant fish live in the Mekong than any other river on Earth… Currently, the Lower Mekong remains free-flowing, which presents a rare opportunity for the conservation of these species. But the clock is ticking."

According to the report, even more is at stake than the fates of the giant fishes of the Mekong River. Construction of the dams are also likely to exacerbate the impacts of climate change on the Mekong River Delta, one of the world’s most fertile regions for agriculture (particularly rice) and one of its most productive for both capture and culture fisheries.

The dams are likely to withhold sediment flowing downstream, reducing the ability of the delta to replenish itself, and rendering it more vulnerable to climate change effects such as increased erosion, saltwater intrusion from sea-level rises, and more intense tropical storms.

This would eventually lead to the displacement of millions of people and the loss of millions' of dollars worth of agricultural land.

Some of these fishes can be seen in a new TV series featuring giant fish.

For more information, see the report: River of Giants: Giant Fish of the Mekong.