How Flashlight Fish Swim Together in the Dark

The fish have organs filled with glowing bacteria that they use to flash.
Sofie Bates, Contributor

(Inside Science) -- A quarter of fish species swim in groups called schools. This behavior is rare at night – but flashlight fish school even in the dark. The fish use special organs filled with bioluminescent bacteria to make create flashes of light. Now, researchers understand how they use this ability to swim together in the dark.

David Gruber, a marine biologist of City University in New York, and his colleagues took a submarine off the coast of the Solomon Islands to see these flashlight fish schooling at night. Then, they made computer models based on the behavior they saw. Their models showed that only 5% of the simulated fish had to be flashning for the group to stay together. And just a few motivated fish could make the entire school change direction. 

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