Light receptors determine the behaviour of flashlight fish

Biologists at the Ruhr-Universität Bochum characterized new, unknown photoreceptors from the bioluminescent flashlight fish Anomalops katoptron. The photoreceptors known as opsins allow the fish to detect light with a specific wavelength. As published on the 11th July 2018 in Plos One the scientists found new opsin variants, which are specialized to detect low intensity blue light in the wavelength range of bioluminescent light emitted by the fish. The blue light can be used to influence the fish behaviour.

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Credit: Stefan Herlitze, RUB-Lehrstuhl Allgemeine Zoologie und Neurobiologie

Flashlight fishes live in schools in the pacific ocean up to a depth of 400 metres.

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The splitfin flashlight fish, Anomalops katoptron, is one of many ocean-dwelling animals that produce their own bioluminescent light using symbiotic bacteria. The fish has light organs located under its eyes such that the light can be turned on and off by blinking, like a flashlight. Little is known about the function and purpose of the Morse code-like blinking patterns displayed by the fish, so a research team led by Jens Hellinger from Ruhr-University in Germany sought to investigate how this enigmatic fish uses bioluminescent illumination.

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The Flashlight Fish Anomalops katoptron Uses Bioluminescent Light to Detect Prey in the Dark.

Flashlight fish blinking in presence of plankton.

This shot shows the brilliance of the bioluminescent organ just below the fish's eye.

The flashlight fish's "light" is produced by symbiotic luminous bacteria that live in the light-emitting organ, called a photophore.

The fish hunts at night, using its photophore to attract prey such as small fish and plankton. The photophore is also believed to be also used for communication.

The fish can "turn off" its light by closing an eyelid-like membrane over its photophore.