Baby reef fish use an internal magnetic compass to find their way home

A study published in Current Biology finds that baby reef fish may have an internal magnetic ‘compass” that can direct them home at night when there is no sun or stars to guide them.

Professor Mike Kingsford of James Cook University collaborated with colleagues in Germany to discover how baby Cardinal fish are able to find their home reef in the darkness of night. During this study, the researchers set up an isolated magnetic field that they could manipulate in order to observe how the fish reacted.

Professor Kingsford noted, “Normally, baby reef fish orientated to the southeast, but when we altered the magnetic field clockwise by 120 degrees, there was a significant change in the direction the fish swam. They all turned further west, thinking they were still on track to their destination.”

Their results showed that fish larvae can use a magnetic sense to point them in the direction of home. Previous research done by this team has shown that these fish begin a “homing process” when they get closer to their target, relying on odor, sounds, and landmarks to find their home reef.

Other studies have shown that birds, marine mammals, sharks, and boney fish have a similar internal compass. However, this most recent study is the first clear indication that baby reef fish use magnetic senses to orient themselves at night.

Reef fish hatch from eggs into larvae and then disperse for days to months out in the ocean before finding another reef or returning home. It is believed that once they find a reef, they generally stay there for the rest of their lives.

Professor Kingsford elaborated, “The study tells us these baby fish actually have brains. They know where they are going and are strong swimmers. As a result, they have some control over the reef they end up on. It’s not just about being led by the currents.”

He thinks that this knowledge can be used further down the road to develop more accurate models of where fish larvae go, which can be used determine the best method for protecting and maintaining sustainable fish stocks.

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Credit: Earth.com author Connor Ertz