U.S. scientists say they've confirmed salmon are using Earth's magnetic field to navigate across thousands of miles of water to find their rivers of origin.

Researchers at Oregon State University report exposing hundreds of juvenile Chinook salmon at the Oregon Hatchery Research Center to different magnetic fields that exist at the latitudinal extremes of their oceanic range.

Fish responded to the "simulated magnetic displacements" by swimming in the direction that would bring them toward the center of their marine feeding grounds, the university reported Thursday.

"What is particularly exciting about these experiments is that the fish we tested had never left the hatchery and thus we know that their responses were not learned or based on experience, but rather they were inherited," study lead author Nathan Putman said.

In the experiment, fish presented with an artificial magnetic field characteristic of the northern limits of the oceanic range of Chinook salmon were more likely to swim in a southerly direction, while fish encountering a far southern field tended to swim north, the researchers said.

The finding proves fish possess a "map sense" determining where they are and which way to swim based on the magnetic fields they encounter, they said.

"These fish are programmed to know what to do before they ever reach the ocean," Putnam, a postdoctoral researcher, said.