Some of the prettiest fish in the oceans and seas glow in the dark. Bioluminescent fish produce their own light through a chemical reaction. The light is usually blue or green and helps fish communicate, lure prey, attract mates, and camouflage themselves in the deep, dark waters. Some of the glowing fish seen around coral reefs include lanternfish, flashlight fish, dragonfish, anglerfish, and more.
Fish that glow in the dark, known as bioluminescent fish, are some of the most fascinating creatures found throughout Earth’s oceans and seas. Bioluminescence is the production and emission of light by a living organism. It results from a chemical reaction during which chemical energy gets converted to light energy. Some fish are able to produce their own light through bioluminescence, usually in shades of blue or green. This glow serves a variety of purposes, including attracting prey, communicating, camouflage, and mating rituals. Some of the prettiest bioluminescent fish live around coral reefs, where their glow contrasts beautifully against the colorful backdrop.
What Causes Fish to Glow?
The glow that bioluminescent fish produce comes from a chemical reaction involving luciferin, the light-emitting pigment, and the enzyme luciferase. Luciferin reacts with oxygen, a process catalyzed by luciferase, to produce light. The fish keeps the luciferin and luciferase stored separately in its body. When it wants to produce light, it mixes the two chemicals together, and the reaction results in the bright glow. The fish can control when and where this reaction takes place, allowing it to glow at will. Some parts of the fish’s body contain higher concentrations of luciferin and luciferase, such as glowing photophores along the sides.
Purposes of Bioluminescence in Fish
Fish glow for a variety of reasons, all tied to survival in the challenging ocean environment:
Camouflage
Fish like the cookiecutter shark glow to blend in with ambient light as they swim in deeper waters. This counter-illumination camouflages the silhouette of the fish when viewed from below. Predators swimming beneath struggle to see the bioluminescent fish swimming above them.
Communication
Deep sea fish use bioluminescent signals to communicate with each other. Different glowing patterns help attract mates, warn others of danger, or mark territory boundaries.
Prey Attraction
Anglerfish and dragonfish utilize glowing lures to attract unsuspecting prey towards their sharp teeth. These glowing extensions wiggle through the water like small fish, luring in larger animals as prey.
Predator Avoidance
When threatened, some fish emit bursts of light to temporarily blind or confuse attackers. This flash gives the fish valuable time to flee and escape.
Pretty Bioluminescent Fish
While bioluminescence occurs across many fish species, some particularly beautiful examples live around coral reefs. The bright blue and green glows of these fish stand out vividly against the colorful backdrops of reef environments.
Lanternfish
Lanternfish comprise over 250 different species and earn their name from the photophores along their bodies that glow like lanterns. They inhabit oceans worldwide at depths up to 1,600 feet. Different species show diverse patterns, shapes, and concentrations of photophores. Some popular species kept in aquariums include the spotted lanternfish and blackfin lanternfish.
Flashlight Fish
The aptly named flashlight fish has a distinctive glowing organ just below its eye. It can control this light organ separately from the rest of its bioluminescence, using it like a headlight to illuminate its surroundings. Flashlight fish live in the Western-Pacific and Indian Oceans, inhabiting reefs and lagoons up to about 200 feet deep.
Anglerfish
Anglerfish include over 200 species like the humpback anglerfish and common black devil. These ominous-looking fish are named for the glowing lure they dangle from their foreheads, used to attract prey towards their giant mouths and fangs. Different species live at varying ocean depths where little food exists – their bioluminescent lures provide a crafty hunting advantage in the darkness.
Dragonfish
The dragonfish is another deep sea predator that uses glowing lures to hunt. Its genus includes over 300 species, like the barbeled dragonfish with its unique chin whisker. Their bioluminescence involves microscopic glowing crystals along a slender rod that projects from near the fish’s mouth. This photophore acts as an irresistible lure to draw in food.
Ponyfish
Ponyfish are named for their elongated snouts, and several species produce their own glows. Schools patrol reefs in the Indian and Pacific oceans, glowing vibrantly at night to confuse predators. Different ponyfish glow in unique shades and patterns. Some frequently encountered species include the slipmouth, brushtooth, and bioluminescent ponyfish.
Where to See Bioluminescent Fish
The clear ocean waters around coral reefs provide some of the best opportunities to spot glowing fish in action:
| Location | Notable Species |
|---|---|
| Great Barrier Reef, Australia | Pinecone fish, flashlight fish, ponyfish |
| Papahānaumokuākea Marine National Monument, Hawaii | Dragonfish, lanternfish, viperfish |
| Sea of Cortez, Mexico | Lanternfish, flashlight fish, grenadier |
| Aquarium exhibitions worldwide | Lanternfish, ponyfish, flashlight fish |
Divers and snorkelers around these reefs have the best chance to encounter bioluminescent fish in their natural habitats. Many aquariums also feature exhibitions spotlighting brightly glowing species in darkened tanks.
Threats to Bioluminescent Fish
While fascinating to observe, many bioluminescent fish species now face increasing threats:
– Overfishing – Commercial overfishing depletes populations, especially deep sea species. Their long life spans and late maturity make recovery difficult.
– Habitat degradation – Pollution, destructive fishing practices, and coral reef damage threaten sheltered glow fish habitats.
– Climate change – Rising ocean temperatures, acidification, and reduced oxygen levels hamper bioluminescent species that have adapted to cold, dark, stable environments.
– Light pollution – Increased artificial lighting along coastlines alters natural light cues that govern bioluminescent behaviors, disrupting feeding, reproduction, and predator avoidance.
Conclusion
Bioluminescent fish comprise some of the most mystical and aesthetically pleasing creatures in our oceans. The otherworldly blue and green glows they produce brighten up the dark depths where sunlight fails to reach. While fascinating to observe, many of these unique fish now face expanding threats. Preserving their fragile habitats and reducing pressures from overfishing, pollution, and climate change remain key to protecting bioluminescent fish populations worldwide. Their magical glows reveal hidden biological processes and provide allure to coral reef environments. With proper stewardship, we can ensure these captivating fish continue lighting up our oceans for generations to come.
