New research suggests that fish can sense magnetic fields—through their noses.
According to a new study appearing in the July 9, 2012 issue of Proceedings of the National Academy of Sciences, for the first time scientists have isolated magnetic cells (magnetoreceptors cells) in fish that respond to Earth’s magnetic fields. The study suggests that fish may be able to detect not only the direction of North based on magnetism, but small differences in magnetic field strength that can give them more detailed information about their position.
For decades there’s been speculation that migratory animals are using geomagnetic cues to get around. New research is now looking for where in the sensory system these signals might be coming from.
“You can have a hypothesis and build a model but you’ve got to then get down and find the mechanism,” said Dr. James Anderson, research professor in the School of Aquatic and Fishery Sciences at the University of Washington. “That’s what they’re doing now.” Dr. Anderson is also researching geomagnetism and fish migration.
Every species that has a long-distance migration has some kind of global navigation sensory system, he explains. In many birds, input is from their visual sensory system, enabling them to determine which direction they’re going by a change in visual properties. The new studies suggest salmon detect their global position with tiny magnets in their noses.
Salmon have the capacity to navigate in the ocean using information from the earth’s magnetic field to find their way back to their natal streams to spawn. Anderson and his team of modelers are able to model and fit the return of spring Chinook to the Columbia River using a high seas navigation scheme where they follow the geomagnetic information lines.
Geomagnetic information lines are like latitude lines, about perpendicular to the earth at the poles and parallel to the earth at the equators and change uniformly between the two. Anderson’s research suggests that, unlike lines of latitude, which only exist on maps, salmon are able to determine latitude by detecting the angle of these geomagnetic lines. Researchers of the new study found that fish can likely feel magnetic inclination through cells in their noses.
Years ago, Anderson said, scientists proposed a hypothesis that young salmon fix the inclination of the geomagnetic field in their memory when they enter saltwater. In the ocean they always have a sense of how far north or south they are of their home stream by comparing the perceived inclination with the remembered inclination. Then after spending several years in the ocean, the fish simply swim along the line to return to find their home stream. Sort of like following “a salmon highway home,” he said.
Many fish, such as salmon, tuna, zebra fish and tilapia, are known to use magnetic sensing to determine direction. Such information is especially useful to guide their long-distance migrations between their foraging grounds and breeding habitats.
The new study found that small iron-rich crystals, most likely of magnetite—the most magnetic of all minerals—are attached to the walls of trout olfactory cells. The crystals try to line up with the magnetic field so a change in the fish direction causes the crystal to pull on the cell wall. In this fashion, fish can sense the Earth’s magnetic field and their latitude. The fish can also use the direction and polarization of sunlight to distinguish east from west.
“Fish navigation is a fascinating subject because the story goes from what happened at the molecular level inside a cell on up to the scale of the earth,” Anderson said.
Migratory species have to be able to carry out their life cycle through what’s been called a migratory triangle: they’re born in one area, migrate to another area to mature, and then return to the same area where they were born to spawn. Understanding these migratory paths and how fish navigate them is fundamental as is understanding how changes in the environment will disrupt these migratory paths.
“We have altered the flows through the Delta so much through pumps and reservoirs; there’s a real concern on getting the fish through the Delta safely,” Anderson said.
That will require the development of models that consider a more complex mix of fish responses to sensory information. In addition to known navigation cues such as the salmon’s well-known sense of smell and the ability to detect minute changes in currents, such models might need to include the ability to sense and respond to magnetic fields. “If we understand better how fish navigate, we can understand how we can improve their migration through the system,” he said.