Flashlight Fish Use Their Glowing Powers to School at Night

Flashlight fish (Anomalops katoptron). The torch-like organ can be seen under its eye. (D. Gruber, 2019)

(CN) – While most fish tend to disperse in dark waters, scientists have discovered flashlight fish – which use bacteria in their organs to glow – have a natural tendency to form schools and use their bioluminescence for signaling.

Scientists used low-light underwater cameras to observe a species of fish known as Anomalops katoptron, commonly referred to as flashlight fish, and discovered a behavior that had never before been observed, according to a study published Wednesday in the scientific journal PLOS ONE.

Researchers sought to understand how flashlight fish navigate at night and how they utilize their biological lighting abilities as a group. They discovered the fish school together with the aid of bioluminescent signals.

A) Time lapse image from the recorded video of flashlight fish. The different intensities are due to fish swimming at different depths. Closer fish are brighter than more distant fish. B) Time stamps, in seconds, corresponding to the flashes. (D. Gruber et. al / PLOS One)

Nearly a quarter of fish populations instinctually school together, but observers had never reported observing fish using their bioluminescence to school.

David Gruber – a professor of biology and environmental science at the City University of New York, who led the study – and a team of researchers found that only a few fish need to actively flash in order to keep the school together at night.

“A computer model of flashlight fish schooling behaviors shows that only a small percentage of individuals need to exhibit bioluminescence in order for school cohesion to be maintained,” researchers said in the study.

This suggests that the lighting abilities of flashlight fish are crucial when using directional messages and signals in order to school.

Researchers theorize some of these unique schooling and lighting behaviors are used for survival purposes. They observed that bioluminescence keeps predators confused and also that a school of flashlight fish that is only partially lit is far less noticeable in darker and more dangerous environments.

The study concluded these new observations of flashlight fish behaviors could be used to help researchers conduct future undersea monitoring experiments.

“Understanding the kinetics of flashlight fish utilization of bioluminescence to school in the dark may also have practical applications in the design of schooling ‘robotic fish’ that can be used for both environmental monitoring applications as well as to study the behavior of other bioluminescent fishes by potentially mimicking luminescence signaling behavior to elicit species-specific signaling responses,” the study states.

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