Bioluminescence occurs when a biological organism produces a chemical reaction where energy is released in the form of light. A familiar example of bioluminescence is the firefly, emitting a yellow-green light. In the marine environment, most bioluminescence appears as a neon, blue glow. Some small organisms in the sea, such as plankton, produce their own chemicals used to create light, commonly seen as glowing waves crashing onto the shore during moonless nights.
Most bioluminescent animals; however, rely on a symbiotic relationship with bacteria to produce the chemical reaction for their host. Marine fishes also depend on bacteria and have developed special organs to house the bacteria called photophores. Bioluminescence in fish serves several functions; prey attraction and capture, predator deterrence and confusion, mate attraction, communication between members of the same species, and navigation and signaling when schooling.
On a moonless night in Matuku, I saw an example of two of these functions; prey attraction and schooling. I turned my dive light off to check the reef for bioluminescent creatures and soon witnessed the bioluminescence of two groups of spots of blue suddenly merge into one large group and dart through the reef in distinct, synchronized movement.
When I turned my light on, the flash of a typical silverside body was all I could see as the fish dispersed and disappeared into the small crevices of the reef.
Shortly after turning my light off again, tiny lines of photophores would appear in a scattered clusters and merge again into a distinctly structured formation of schooling fish.
When the school left I noticed a small glowing ball off in the distance. Swimming slowly through the dark toward the neon glow, I saw a pair of alien-like eyes take shape; the creature appeared to be a swimming back and forth. The light organs themselves also open and close differently during day, night, and feeding. During the night, however, the light organs were closed only half of the time. A simple summary is shown below. To see the full dataset, go to the paper here. The above graphs were created by Sciworthy and show a simplified summary of the data.
Please visit the full paper for the real figures. This is the first time the flashlight fish blinking patterns and feeding behavior has been rigorously tested and described. But the splitfin flashlight fish wields bioluminescence differently.
In a new study , researchers led by Jens Hellinger, a zoologist at Ruhr-University Bochum in Germany, show how this fish uses its bioluminescence to spot prey in the dark.
Photo by Jens Hellinger. Splitfin flashlight fish have one bean-shaped cavity under each eye, making them look like football players sporting eye black.
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. Nearly a quarter of fish populations instinctually school together, but observers had never reported observing fish using their bioluminescence to school.
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