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When the annual rains return to the Amazon, the raging river swells and flows rapidly. For the dorado fish, that rising tide is a millennial correction: it’s time for a homeward journey that spans the continent.
Its 7,000-mile round trip is the longest freshwater journey on Earth — and one of the most dangerous.
Scientists have discovered the full extent of its odyssey in recent years. Dorado, which is part of the “Goliath” catfish family and also known as the gilded catfish, spawns on the slopes of the Amazon River in the Andes. The larvae drift thousands of kilometers downstream to the river, where the river meets the Atlantic Ocean. The nutrient-rich waters are the perfect place for baby dorado to feed and grow — up to six feet long and 200 pounds — before making the 1-2 year journey back to the foothills of the Andes to spawn, and start the cycle all over again.
But the same path that the dorado has followed for thousands of years is now being choked by hydroelectric dams and river divides, preventing the fish from reaching their breeding grounds and causing severe population declines.
A new international action plan, presented by Brazil at the United Nations-sponsored Convention for the Conservation of Migratory Species (CMS) and signed yesterday aims to change that trend, uniting six countries in an effort to keep the river connected and giving the dorado – and six other species of migratory Goliath catfish – the opportunity to complete their journey home.
Dr. “(Dorado) is incredibly important to people who live along the Amazon River,” says Zeb Hogan, a professor of biology at the University of Nevada and freshwater fisheries advisor for CMS.
“We need to bring everyone together, to try to work together to find a way to protect these amazing animals.”
Migratory species are difficult to protect because they cross international borders; The dorado is found throughout nine countries in South America.
What is happening in one part of the river throughout the entire system: in 2019, studies found that the numbers of dorado in Bolivia, one of the places where catfish spawn, dropped by 80% in 15 years after two dams were built below Brazil.
They are in danger of disappearing in this upper part of the river completely, but it also has a strong effect downstream: the dorado is the main predator, which keeps the small species of species and the whole environment of the river balanced.
More careful planning for future hydropower projects, including assessments of their impact on migratory fish from the outset, can help reduce risk and improve site selection, says Hogan.
For existing ponds, interventions such as fish ladders—a structure or channel that allows fish to migrate around or into the pond—or removing old or unused ponds can help close migration routes, Hogan says: “Scientists have been surprised how quickly these migratory fish can return when given the opportunity to navigate the system.”
Migratory fish such as dorado are also important for local food security, economy and cultural heritage.
“Species such as dourada, piramutaba and other catfish are highly valued because of their size and quality of food,” Dino Delgado, leader of commitment and strategy of the Wildlife Conservation Society (WCS) and Amazon Waters, told CNN in a message.
About 47 million people live in the Amazon region, and its fisheries rely heavily on migratory species, which account for 93% of the catch and generate $436 million a year, according to CMS.
In addition to hydroelectric dams, Amazon fish face additional pressure from mercury pollution from mining, and overfishing.
In an open letter to the CMS delegation, fishermen in the state of Madeira – one of the most disturbed parts of the Amazon river due to the two large dams in Porto Velho – stressed the need for “joint and urgent action” from governments, adding: “The international effort will be successful only if it is accompanied by fishermen, Amazon natives and natives.”
Delgado, who worked closely on the development of the action plan, says that with the approved plan, important work will begin – from combining local scientific and indigenous knowledge about important habitats, to environmental efforts to validate data collection.
Cooperation between the six countries of Amazonia is an “important interest” for the conservation of biodiversity that will strengthen scientific knowledge and harmonize policies and regulations throughout the region, Guillermo Estupiñán, expert on wetlands and water resources at WCS Brazil, told CNN in an email.
The dorado – along with the laulau “Goliath” catfish, which can grow up to 12 meters in length and weigh 400 kilograms – was added to the CMS protection list in 2024 – a step that laid the foundation for the action plan currently accepted, says Amy Fraenkel, CMS executive secretary.
“For other species, there are these kinds of cooperative agreements under CMS,” says Fraenkel, pointing to the Central Asian mammal effort as a successful example. But we haven’t done that yet [previously] it did for freshwater fish, which is why this model is so powerful.
The battle of the dorado indicates a global crisis. The CMS report, released at the organization’s meeting in Brazil last week, analyzed data on 15,000 species, identifying 325 species of migratory fish that require international protection.
Asia, with 205 listed species, was marked as a place of migration, especially in the Mekong Delta where one of the largest freshwater fish in the world, the Mekong giant catfish of 300 kilograms, migrates hundreds of kilometers.
Hogan compares the migration of wildebeest and wildebeest across the Serengeti, Tanzania. “You have the same number of living creatures that move underwater, and you wouldn’t know it; you wouldn’t see it,” he says. However, none of the Lower Mekong countries participate in this alliance, a gap that Hogan sees as a “long-term opportunity.”
Globally, the number of migratory freshwater fish has declined by 81% since 1970. Fish are often neglected in conservation because they are viewed primarily as food, as opposed to a “biodiversity issue,” Hogan says, adding that rivers are often managed as a resource, despite the fact that 47% of the world’s water is covered by land. According to the UN, about 70 percent of the countries that are members of the United Nations that share waterways between two or more countries do not have comprehensive cooperation agreements to manage them, and they leave marine life at risk of uncertain protection.
“Rivers know no boundaries — and the fish that depend on them,” said Michele Thieme, vice president and director of clean water for WWF-US, in a press statement. “Rivers need to be managed as interconnected systems, with cooperation across borders, and investment in comprehensive drainage solutions now before these flows are lost forever.”
Back in the Amazon Basin – home to at least 2,700 species of freshwater fish, more than anywhere else in the world – research has found 20 migratory fish that meet CMS criteria for protection.
Despite the “alarming” decline, Hogan sees the species report’s list as “325 opportunities to work together,” and the Amazon catfish plan gives him new reason to cautiously hope that change is near.
He adds: “This is a model that we did not have 10 years ago for freshwater fish.
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