Eerie ice-blue lights wink on and off in pitch-dark waters. Welcome to Wild Reef’s flashlightfish exhibit.

flashlightfish“Bioluminescence”—the production of light by a living organism—even sounds spooky. Living things that glow in the dark? The sea is full of them, especially the deep ocean. The light emitted is usually blue or blue-green. Blue light travels best through water, and most marine organisms can detect it.

In their native Philippines waters, these flashlightfish shun the sun, hiding during the day at depths of 65 to 165 feet. At night, they come out to feed, moving up reef walls to shallower areas. Moonless nights are their favorite time to hunt, when they lure tiny planktonic prey toward their blinking lights and straight into their mouths. They also eat smaller fishes attracted to the plankton.

If you look closely, and wait about 30 seconds, you’ll see the flash of a fish’s light organ, a bean-shaped pocket under either eye. The pocket is filled with billions of symbiotic bacteria that live on sugar and oxygen from the fish’s blood and emit a biochemical light as a by-product.

If the light were present all the time, flashlightfish themselves would be easy prey in the dark. But each pocket has a black membrane that can be raised, like an eyelid, to block the nonstop illumination. A fish “blinks” two or three times a minute. The light is also a visual Morse code for attracting a mate and for communicating within schools of 20 to 200 fish.

When pursued by a predator, flashlightfish use a “blink-and-run” defense. The fish take off, flashing up to 75 times a minute and zigzagging so that the predator can’t zero in on any one fish. At some point, the school changes direction, turns off the lights and swims away safely.

Have you come this far unscathed? Then check back tomorrow to see what else might have its lures set—for you?—in Wild Reef.

 —Karen Furnweger, web editor

Not spooky enough? Check out our previous Halloween blog posts!