This 6-foot-long, 200-pound catfish is a goliath—and makes an epic migration

When Ronaldo Barthem began studying the dorado, a type of goliath catfish, in an estuary of Brazil’s Amazon River several decades ago, he was puzzled by the absence of adult fish. Where, he wondered, did the golden-hued animal, which can grow up to six feet long, go to spawn?

Years of investigation revealed a stunning answer: The dorado swims through several countries, all the way to the foothills of the Andes on the opposite side of the continent, to complete its life cycle. The 7,000-mile roundtrip journey is by far the longest migration made by any freshwater fish in the world, according to recently published research in the journal Fish and Fisheries.

The epic migration has likely helped the dorado increase its growth and survival, as young animals on the move benefit from a huge diversity of foods, from algae to insects. But its lengthy journey across national borders has also made the species, which may weigh more than 200 pounds, more vulnerable to human threats, from overfishing to hydropower dams. 

These are the same reasons migratory freshwater fish have declined by 76 percent since 1970, ranking them among the most endangered groups of animals in the world. (Read why we still haven’t caught the biggest freshwater fish.)

Despite their dire situation, migratory fish have historically been offered little protection. Of the 1,200 animals listed in the Convention on Migratory Species, a UN-governed international treaty, just two are migratory freshwater fish: the critically endangered Mekong giant catfish and the lake sturgeon.

That number, though, doubled in February, when the dorado, along with another goliath catfish from the Amazon, the piramutaba, became the first two fish species from the Southern Hemisphere to be covered under the treaty.

The news was greeted enthusiastically by many fish experts, including Barthem, an ecologist with the Goeldi Museum in Belém, Brazil: “It’s perhaps the most promising initiative to promote the conservation of the aquatic ecosystems” in the Amazon, he says.

For instance, the listing could promote collaboration between governments across the species’ migration route, leading to better conservation plans, says Susan Lieberman, vice president for international policy at the Wildlife Conservation Society in the U.K.

A richness of migratory fish

As apex predators, the Amazon’s seven species of goliath catfish play a fundamental role in the balance of the river system. What’s more, migratory fish account for 80 percent of the Amazon’s commercial fish production; both artisanal and industrial fisheries closely track the seasonal movements of the dorado and piramutaba.

For the new study, researchers also relied on catch data, larval studies, and field observations to gain insight into these fishes’ movements. (Learn how a species is found daily in the Amazon.)

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The life of the dorado begins close to the Andes, where the fish are born before they drift as larvae and juveniles downstream toward the mouth of the river. The fish, which can live up to 17 years, later return as sub-adults to the western Amazon to spawn, crossing several countries, including Brazil, Bolivia, Colombia, Ecuador, and Peru. The smaller piramutaba makes similar, if shorter, migrations, though its exact spawning grounds are unknown.

“Homing, a behavior that causes these fish to return to the place where they were born to spawn, indicates that this may be a memory that resists distance and the different environments along their migratory routes,” says Guillermo Estupiñán, a goliath catfish expert with the Wildlife Conservation Society in Brazil.

The massive annual flood pulse that transforms the Amazon and its more than a thousand tributaries, submerging forest-covered wetlands and creating a mosaic of different habitats, also favors the migratory behavior of fish in search of breeding or feeding grounds. 

The recent study in Fish and Fisheries showed there are at least 223 species of migratory fish in the Amazon, but the true number is probably far higher. (Read about another enormous fish that undertakes a long migration.)

For the goliath catfish, overfishing remains a main concern: In 2007, scientists estimated an annual dorado harvest of at least 10,500 tons in the Amazon Basin. Brazil has not updated such statistics since, though there are plans to resume monitoring, says Lisiane Hahn, a fish biologist who runs a Brazilian company called Neotropical Environmental Consulting.

But hydroelectric dams may present a more existential threat. While no dams exist on the main stem of the Amazon, there are long-standing plans to build hundreds of them throughout the rest of the river system—structures that could cut off migration routes for goliath catfish. (Learn how megadams threaten the world’s biggest fish.)

Hahn spent eight years tagging and tracking hundreds of dorados and piramutabas in the Madeira River after two hydroelectric dams were built there in 2012. She found not a single fish could bypass the dams. As a result, the dorado population has drastically declined in the headwaters of the Madeira in Bolivia, her research shows.

Just the beginning

The Convention on Migratory Species maintains two lists: one for species threatened with extinction, and a second for species that move across national borders and rely on international cooperation for their survival. The two goliath catfish, which are not yet at risk of going extinct, were added to the second list.

Scientists have called for global “swimways,” like animal-migration corridors on land, that would protect key migratory fish habitats. Barthem and others also hope more migratory fishes will gain listing under the convention, with almost 900 species making at least partial migrations in fresh water, the criteria for such an inclusion. (Read more about how scientists are saving megafishes.)

Barthem, who was instrumental in mapping the epic dorado migration, adds new technologies will bring new insights to studying Amazonian fishes’ amazing journeys.

“We are just beginning to understand these migrations,” he says.

Stefan Lovgren is a regular contributor to National Geographic and the co-author with Zeb Hogan of the 2023 book “Chasing Giants: In Search of the World’s Largest Freshwater Fish.”