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.
In their recently published PLOS ONE study, the researchers examined the blink frequency of a school of flashlight fish under different laboratory conditions. They found that during darkness at nighttime, the flashlight fish blinked very frequently, at 90 blinks per minute, with the light being on and off for an approximately equal amount of time, as shown in the video clip below.
When the flashlight fish detected living planktonic prey in the experimental tank at night, their light organs were opened for more time, keeping the light on longer, and they blinked five times less frequently than in the absence of prey, as shown in the video clip below.
The authors suggest that the flashlight fish reduce their blinking and keep their light organs open so that they can produce more light to detect and feed on prey. They recommend additional field research to see whether the fish display the same behavior under natural conditions.
Image and Videos: Hellinger et al (2017)
Reference: Hellinger J, Jägers P, Donner M, Sutt F, Mark MD, Senen B, et al. (2017) The Flashlight Fish Anomalops katoptron Uses Bioluminescent Light to Detect Prey in the Dark. PLoS ONE 12(2): e0170489. doi:10.1371/journal.pone.0170489