The World Wide Fund for Nature’s (WWF) latest report has determined that at least 1,148 fish species, or around 25 per cent of the inland fish on the planet, are found nowhere else on Earth but in the Mekong River.

In “The Mekong’s Forgotten Fishes”, released today, the WWF explained that the Mekong is the world’s largest inland fishery. It sustains at least 40 million people and is valued at around $11 billion every year.

But the report added that 19 per cent of the assessed fish species are threatened with extinction, including mega and migratory species.

The Mekong is the third most biodiverse river, after the Amazon and Congo.

This first-of-its-kind report celebrates this wealth of species – from the world’s largest freshwater fish to one of its most minute, from ones that “talk” or “walk”, to fish that spit water to knock unsuspecting prey into the river.

The Mekong is also home to one of the largest migrations on Earth, in terms of numbers of animals, with an estimated 5 billion fish on the move each year.

The report said the Mekong’s fish continue to be undervalued and overlooked by decision makers. At least 19 per cent of assessed species are now estimated to be heading towards extinction, while 18 species are already listed as critically endangered on the IUCN Red List of Threatened Species.

“The alarming decline in fish populations in the Mekong is an urgent wake-up call for action to save these extraordinary – and extraordinarily important – species, which underpin not only the region’s societies and economies but also the health of the Mekong’s freshwater ecosystems,” said Lan Mercado, WWF Asia-Pacific Regional Director.

In recent years, Cambodia has been confirmed as home to some extremely rare examples of the Mekong mega species, including the catfish (Pangasianodon gigas) and Mekong giant bard (Catlocarpio siamensis).

The most spectacular catch was the the record-setting giant stingray (Urogymnus polylepis) which was discovered in Stung Treng province in June 2022. At 3.98m in length and 2.2m in width, the 300kg specimen was the largest ever measured by researchers.

The stingray was recognised by the Guinness World Records as the largest freshwater fish on record.

It was released back into its natural habitat, in the depths of the Mekong.

According to the report, a combination of threats are causing a serious decline in the Mekong’s fish population, including habitat loss, hydropower dams which fragment free flowing rivers, the conversion of wetlands for agriculture and aquaculture, unsustainable sand mining, invasive species and climate change.

“Mekong fish have swum through our civilisations and cultures for millennia and millions of people still depend on them every day,” said Mercado.

“We must act now to reverse this disastrous trend because the communities and countries of the Mekong cannot afford to lose them,” she added.

Environmentalists were optimistic that this year will see the region turn the tide and start to reverse decades of decline in Mekong fish populations. They urged each country along the Mekong to join the Freshwater Challenge – the largest freshwater restoration and protection initiative in history.

Zeb Hogan, of USAID’s Wonders of the Mekong project, urged closer consideration for the future of the region at a decision-making level, while also building expertise and knowledge in local communities.

“The good news is that it’s not too late to restore the Mekong and bring its fishes back from the brink,” he said.