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Fish appear to steer with magnets

Scientists have zeroed in on the likely source of some animals' sense of direction. Rainbow trout seem to be guided by an 'internal compass' of sorts.

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Kenneth Lohmann, a distinguished professor of biology at the University of North Carolina who studies animals' magnetic sense, said the new results have ramifications beyond the realm of rainbow trout.

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"If the authors are correct that the magnetite they have found is involved in detecting magnetic fields (which seems likely), then … this might have important implications for how other animals perceive magnetic fields," Lohmann told LiveScience. "It is quite possible that similar magnetite crystals are involved in detecting magnetic fields in numerous animals." It is also possible that there are two or more types of magnetoreceptors that evolved separately, he said.

The work may also lead to more rapid advances in the understanding of animal migration simply by demonstrating a new technique for identifying magnetic cells — that is, they subjected tissue to a rotating magnetic field, which made magnetic cells start spinning and be easily spotted.

"For about 30 years now, many researchers have suspected that at least some animals use microscopic crystals of the mineral magnetite to sense magnetism," Lohmann said. "A major problem, however, has been that the magnetite particles in animals are tiny, and finding them under a microscope has proved to be exceedingly difficult.  The new technique described in the paper may make it much easier to identify magnetite-containing cells." [Vision Quiz: What Can Animals See?]

Part of the challenge was that only one in 10,000 nasal cells is magnetic, Winklhofer said. The fact that magnetism is dispersed through the animals' nasal tissues is part of what makes it work so well: "If they were as closely packed as photoreceptor cells in the retina or as hair cells in the inner ear, then they would interfere strongly with each other, because their internal compass needles would produce a locally strong magnetic field, which would be felt by the neighboring magnetic cells. Such a proximity would deteriorate the magnetic sense."

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