When the larvae hatch, currents carry them north-northwest, and experiments have shown that they consistently swim south-southeast guided by the sun back to their birthplace. But to see whether magnetic forces are also at work, the researchers tested them by using a device that creates a uniform magnetic field whose direction can be manipulated.

With the larvae in a tank surrounded by the device, the scientists turned the earth’s normal magnetic north 120 degrees clockwise. The fish followed right along, swimming in the direction the researchers steered them. The study is online in Current Biology.

The lead author, Gabriele Gerlach, a professor of marine biology at the University of Oldenburg in Germany, said that many other marine fish and invertebrates “have the same behavior — they hatch and then are washed out into the ocean for days, weeks, even months. And they might have this same magnetic orientation behavior.”