After spending 3 years at sea and traveling up to 300 kilometers away from home, a rainbow trout can swim straight back to its original hatching ground, following freshwater streams inland and rarely heading in the wrong direction. This remarkable feat of navigation likely relies on many senses; the fish have superb eyesight and smell. But the trout also seem to rely on Earth’s magnetic fields, which point them in the right direction. Now, for the first time in any animal, scientists have isolated magnetic cells in the fish that respond to these fields. The advance may help researchers get to the root of magnetic sensing in a variety of creatures, including birds.
Previous research has shown that many species of fish, as well as migratory birds, have the ability to detect differences in magnetic field strengths, which vary around the globe. Scientists think that the key to this ability is magnetite, the most magnetic of all minerals, which they’ve found embedded in bird and fish tissues. They’ve even narrowed down which tissues in these animals could contain magnetite by using dyes that bind to the mineral. But they’ve never been able to isolate individual cells that contain magnetite, and some of the staining methods have led to false positives and controversy in the field.
In each isolated cell, the magnetite particles were next to the cell membranes, the scientists report online today in the Proceedings of the National Academy of Sciences. And surprisingly, the magnetism in each cell was tens to hundreds of times stronger than researchers had hypothesized, says Winklhofer. This suggests that the 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 precise latitude and longitude.