German scientists have discovered that the flashlight fish uses its own bioluminescent light to hunt prey, according to a study recently published in the open-access PLOS ONE journal.
The splitfin flashlight fish (Anomalops katoptron) produces its own bioluminescent light using symbiotic bacteria. There are light organs under its eyes which it uses to produce light that can be turned on and off by blinking, similar to a flashlight. Presently, little is known about the function and purpose of the fish's blinking patterns.
Hence, Ruhr University Bochum's Jens Hellinger and his colleagues sought to find out more about how the fish utilise its unique ability of bioluminescent illumination. They studied the blink frequency of a school of flashlight fish under a range of laboratory conditions. Their observations indicated that during the night, the fish blinked very frequently in the dark (at 90 blinks per minute), with the light being on and off for an approximately equal amount of time.
However, when these fish detected zooplankton in the tank, their light organs were opened more frequently, keeping the light on longer; and they blinked five times less frequently. When feeding, the light would emit a continuous glow.
During the day, the fish remained in a dimly lit cave, with the light organs closed most of the time, blinking only briefly.
The findings suggest that the splitfin flashlight fish reduced their blinking and kept their light organs open to produce more light so as to detect and feed on prey. According to the scientists, additional field research is needed to see whether the fish displayed the same behaviour under natural conditions.