Migratory freshwater fish, including species that traverse rivers, lakes, and ponds over vast distances, are facing unprecedented threats.

Dams, pollution, and overfishing are blocking their routes, preventing these fish from reaching crucial breeding grounds.

The golden mahseer and goonch catfish are among 30 flagship species highlighted in a new United Nations report as priorities for global conservation. These species are part of a broader assessment covering over 15,000 migratory freshwater fish—half of all fish species worldwide.

Dramatic Declines in Migratory Fish Populations

The report revealed that populations of migratory freshwater fish have dropped by an estimated 81% over the last 50 years. Experts warn that this group has long been overlooked, despite being critical to human livelihoods.

“Freshwater fish support hundreds of millions of people around the world, so for humans, they’re very important,” said Dr. Zeb Hogan, co-author of the report and professor of biology at University of Nevada, Reno.

Migratory fish not only provide sustenance for over 200 million people globally but also contribute to immense biodiversity that requires urgent protection.

“You have fish that can get over 650 lb (295kg) that can migrate over 7,000 miles. Every shape and size of animal you can imagine, these beautiful golden dorado that make long-distance migrations in South America, tropical eels that are moving thousands of miles in Oceania,” he said.

The UN first assessed migratory fish in 2011, evaluating only 3,000 species. Since then, the International Union for the Conservation of Nature (IUCN) has gathered extensive data on thousands more species. This latest review examined the status of over 15,000 fish, identifying 325 species in urgent need of monitoring and protection under a global conservation agreement.

Among these, 30 species were deemed top priority due to both their threatened status and cultural significance, including UK-native species like Allis Shad, River Lamprey, Brook Lamprey, and Atlantic Salmon.

“For example, the golden mahseer is [an] iconic fish of the Himalayas. It’s called the tiger of the river, and many of the people in that region value that fish for cultural and spiritual practices that go far beyond the economic values,” explained Michele Thieme, deputy lead for freshwater at World Wildlife Fund US, who also worked on the report.

“Habitat loss includes things like dams that fragment a river system, and can change the natural flow regime of a river, which results in fish not being able to connect to their spawning habitats,” Thieme said.

Barriers to Migration: A Growing European Concern

Disruption to migratory routes is particularly severe in Europe, where fish encounter a man-made barrier approximately every kilometre. Many of these obstacles—such as culverts and weirs—are unnecessary and could be removed, according to Dr Janina Gray, Head of Science at WildFish.

“It can have a massive impact in terms of the energy reserves fish are using to get over the [barriers].”

However, the cumulative effect of these barriers poses a significant threat to fish populations, she says.

That makes them more susceptible to disease. They’re more likely to get predated. They will spawn in suboptimal grounds.”

Migratory freshwater fish often travel across national borders during their migrations. Coordinated international action is essential to protect these species and restore national fish stocks. Prof Hogan, co-author of the UN study, emphasises the importance of governments working together to tackle overfishing and habitat loss.

The Convention on Migratory Species: A Model for Fish

The UN’s Convention on the Conservation of Migratory Species, established in 1979, encourages countries to protect migratory animals through international cooperation. The UN is now proposing the inclusion of the 30 priority fish species at its annual meeting in three years, following a successful precedent with the Saiga antelope.

After a 2015 mass die-off, coordinated international action helped Saiga populations rebound to over one million. Experts now hope migratory freshwater fish can benefit from similar protection efforts.

“The focus has clearly been on some of the more well known, more visible species, such as the big cats, on antelope, on whales, on dolphins,” said Amy Fraenkel, the UN Executive Secretary for the Convention on Migratory Species (CMS).

The Urgent Need to Protect Freshwater Biodiversity

Historically, the convention has focused on mammals, leaving fish and insects relatively unprotected. Conservationists argue that the time has come to prioritise migratory freshwater fish, whose survival is critical for both ecological balance and human communities worldwide.

At Natural World Fund, we understand that the decline of migratory freshwater fish is a critical wildlife and environmental issue. Protecting these species, restoring rivers and wetlands, and addressing the threats of pollution, dams, and overfishing are vital to preserving biodiversity and maintaining healthy ecosystems for generations to come.

If you care about restoring native wildlife in the UK, support the work of Natural World Fund today.