Magnetic trout snout

SMALL PRINT:How do trout get about? Magnets in their snouts help. A new study in the Proceedings of the National Academy of Sciences has characterised magnetic cells in the fish nose. It's not a new concept that animals could make use of Earth's magnetic field to navigate, but the paper describes a way of identifying cells with magnetic inclusions.

Researchers took cells from the nose of rainbow trout because that was a site where magnetic sense was thought to be at play. When they put a suspension of the cells under a microscope and subjected them to a magnetic field rotating slowly in the plane of focus, a tiny number of the cells rotated too, and they seemed to contain iron-rich inclusions connected to the cell membranes.

The study also found the magnetic dipole moment of the cells was surprisingly large, but researcher and study author Prof Michael Winklhofer, of Ludwig Maximilians University, in Munich, says it makes sense.

“If you want to orient by the magnetic field, you need a pretty strong internal compass,” he says. “This explains why magnetic cells are dispersed. Each magnet produces a magnetic field – if the cells are too close together, they interfere with each other.

“We are now in a position to harvest these much sought after cells and thoroughly study their cell biology,” says Winklhofer. “Still, understanding orientation and navigation in animals will require more than that – it is the brain that integrates all sorts of cues into a mental representation of space.”