ABOVE: An adult flashlight fish (Anomalops katoptron) has pockets under its eyes that are filled with bioluminescent bacteria.

Flashlight fish (Anomalops katoptron) coordinate their nighttime swims by signaling to each other with bright flashes of light, researchers reported August 14 in PLOS One. The team traveled to the Solomon Islands to dive among dense assemblages of flashlight fish—schools made up of hundreds to thousands of individuals. Specialized organs under the fishes’ eyes hold bioluminescent bacteria that the animals use to generate light signals and communicate with each other. By observing and modeling the school’s movements, the researchers learned that less than 5 percent of the fish need to flash for the entire assemblage to maintain formation.

“Over 25% of fish species exhibit collective schooling behavior, but schooling based on bioluminescent signaling has not previously been demonstrated,” says coauthor...

Footage of schooling flashlight fish

D. Gruber et al., “Bioluminescent flashes drive nighttime schooling behavior and synchronized swimming dynamics in flashlight fish,” doi:10.1371/journal.pone.0219852, PLOS One, 2019.

Nicoletta Lanese is an intern at The Scientist. Email her at nlanese@the-scientist.com.

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