Better known for slipperiness than stamina, the American eel was unmasked Tuesday as a stealthy, ultra long-distance swimmer.

For the first time ever, scientists tracked a single eel making the 2,400-kilometre (1,491-mile) trek from Canada's east coast to the Sargasso Sea in the North Atlantic Ocean.

This provided the first evidence that eels are capable of swimming so far.

The Sargasso Sea, near Bermuda, has long been assumed to be the American eel's sole spawning ground, given the presence there of eel larvae.

But more than a century of research has failed to observe an adult eel in the spawning area or swimming in the open ocean.

Adult eels have hitherto been found only in inland rivers in North America and Europe, and the snake-like fish's migration has remained a "complete mystery", said a study in the journal Nature Communications.

For the study, researchers in Canada fit satellite transmitters to 38 adult eels collected from rivers and estuaries in Nova Scotia, released them from the coast, and tracked their movement.

Twenty-eight of the tags transmitted data home, of which eight made it to the open ocean, the team said.

Two of the eels were eaten by predators, while a lone eel was tracked all the way to the Sargasso Sea -- over a period of 45 days.

"This study represents a significant step in understanding the migrations of this most enigmatic of species," the researchers wrote.