Appearance
Flashlightfish have a symbiotic relationship with glowing bacteria, which means that they need each other to survive. The fluorescent bluish-green glow under a flashlightfish’s eye comes from billions of bioluminescent or glowing bacteria that live under the fish’s skin in a bean-shaped photophore or light organ. The bacteria biochemcially produce this light. This built-in light helps the fish hunt, navigate, communicate and avoid predators. In return, the bacteria get a safe home, along with oxygen and nutrients they receive from the fish’s blood. Without a steady supply of oxygen, the bacteria wouldn’t be able to glow.

The almost black coloring of the flashlightfish in contrast to the glow of the photophore makes it hard to distinguish the fish’s shape. This is one way the flashlightfish camouflages itself in the dark waters of night. To escape predators in hot pursuit, this flashlightfish turns off its beam by covering its light organ with a film—like pulling down a window shade. When it does this, it seems as though the fish disappears. Other species of flashlightfish rotate the organ back into their head until it disappears rather than covering it.

Flashlight can be up to 5 inches (12 cm) long. They are sexually dimorphic, which means the males and the females look different. The females are significantly bigger than the male.

Habitat
At depths of 17 to 163 feet (5 to 50 m), schools of flashlightfish live along seaward reefs along steep reef dropoffs with caves. They are nocturnal, which means they are active at night. Flashlightfish hide in caves during the day and venture out at night to feed. When there isn’t much light from the moon, flashlightfish will be found in shallower waters.

Range
Flashlight fish live in the warm waters of the Pacific Ocean, Indian Ocean, and Red Sea.

Diet
Like moths drawn to a flame, zooplankton or tiny animals flock around the glowing face of a flashlightfish. Not only will the flashlightfish eat the zooplankton, but soon, small fish will swim on up to eat them too. Only seeing the glow and not the fish, the flashlightfish nabs the smaller fish. Flashlightfish will also eat small crabs and shrimp.

Reproduction
A pair of flashlightfish lives in a small territory on the reef. Since the female is larger, she protects the male. If there is an intruder into their territory, the female will cover her light, swim right up next to the intruder and then expose her light, scaring them into leaving.

A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

Threats and Management
Since they are active at night and are often found in deep waters, it is hard for collectors in the pet trade to catch flashlightfish.

Did You Know?
Flashlightfish escape in a blinking mass of confusion. With a predator in hot pursuit, flashlightfish blink their lights, zigzag away, and then blink again. This blink-and-run defense makes it impossible for predators to pick out one fish from a flashing group of 20 to 200. This defense strategy seems to work. Scientists have rarely found flashlightfish in the stomach of larger predator fish.

Flashlightfish usually blink two or three times a minute. When they’re fleeing danger, it’s more like 75!

Fishers use flashlightfish to help them fish. They catch the flashlightfish and remove the photophore, using it as a fishing lure to attract fish.

The light that a flashlightfish emits can be seen from over 100 feet (30 m) away. They have the largest photophore with the brightest glow of almost any bioluminescent organism.

References
Web Sites:
NOTE: The following Web sites are not maintained by the John G. Shedd Aquarium and will open in a new browser window.

Fishbase:
http://filaman.uni-kiel.de/Summary/SpeciesSummary.cfm?
ID=7185&genusname=Photoblepharon&speciesname=palpebratus

Print Publications:
Banister, K. & Campbell, A. 1988. Encylopedia of Aquatic Life. New York, New York: Equinox (Oxford) Ltd. 349p. ISBN# 0-8160-1257-101-X.

Debelius, H. 1999. Indian Ocean Reef Guide. Frankfurt, Germany: IKAN. 321p.
ISBN# 3-9317-0267-7.

Hoover, J.P. 1993. Hawaii’s Fishes. A Guide for Snorkelers, Divers and Aquarists. Honolulu, Hawaii: Mutual Publishing. 183p. ISBN# 1-56647-001-3.

Kuiter, R.H. 1998. Photo Guide to Fishes of the Maldives. Australia: Atoll Editions. 257p. ISBN# 1-876410-18-3.

Myers, R.F. 1999. Micronesian Reef Fishes. Barrigada, Guam: Coral Graphics. 216p.
ISBN# 0-9621564-4-2.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

Reader’s Digest. 1984. Reader’s Digest Book of the Great Barrier Reef. Sydney, Australia: Reader’s Digest Services Pty Limited. 384p. ISBN# 0-949819-41-7.

Vocabulary Words

Bioluminescent – A glowing light produced by a living thing.


Extinction – An organism that has not been present on the face of the earth for over 50 years.


Nocturnal – Active at night.


Organism – A living thing.


Pet trade – An industry or business in which animals are taken from the wild and sold to pet stores, zoos, and aquariums.


Photophore – An organ that emits light.


Sexually dimorphic – In animals when each sex is distinctly different. Males look very different than the females.


Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.


Symbiotic relationship – Symbiosis – In order to survive, certain creatures form partnerships with other kinds of animals or plants for feeding, housing or protecting one another.


Zooplankton – Microscopic animals that float at the mercy of the ocean currents and have weak swimming ability.