February 27, 2011

Strange BiologyAn Unusual Fish that Lives Deep in the Ocean

Deep sea anglerfish use a bioluminescent lure to capture prey. (Photo credit: Peter David/Taxi/Getty Images)

The female deep sea anglerfish uses a bioluminescent “lure” that dangles over her head to attract prey. However, her lure isn’t just used to capture food to eat. Male anglerfish use the female’s light source to make sure she’s a member of the same species before he latches onto her as a lifelong mate.

There are more than 200 species of anglerfish that live within the Atlantic and Arctic oceans. Though many live at depths of nearly 1000 meters beneath the ocean’s surface, a few species inhabit the shallow waters of tropical habitats.

Female and male anglerfish look quite different from one another. Only females have a lure above their heads. The lure is actually a portion of the female’s dorsal spine which glows a blue-green color due to the presence of bioluminescent bacteria. Because their rounded shape makes them poor swimmers, an anglerfish typically lies in wait for its prey, waving the lure back and forth slowly. In addition to its unusual headgear, the female also features a ferocious mouthful of sharp teeth that angle inward, which helps prevent prey from escaping once the food is in its mouth. The fish are also able to open their jaws wide enough to swallow prey twice their size, allowing them to make the most of each meal.

In comparison to females, male anglerfish are much smaller in size. In fact, one male anglerfish specimen holds the title as the world’s smallest vertebrate, measuring in at just 6.2 millimeters in length. As the male anglerfish matures, its digestive system begins to deteriorate, rendering it basically unable to get the nutrients it needs to live. To survive, the male anglerfish must find a mate. A pair of nostrils and a set of large eyes dominate a male anglerfish’s face. It uses its nostrils to sniff out the scent of pheromones that announce the presence of nearby female anglerfish. It uses its large eyes to ensure that the anglerfish it sees is a member of the same species. Once it has found a mate, the male latches onto the female’s back, belly, or side by biting it with its own set of sharp teeth. It’s at this point that things get really interesting.

This female anglerfish has two males attached to its body. (Photo credit: Darlyne A. Murawski/Peter Arnold, Inc./Alamy)

Once the male bites the female, the male releases enzymes that cause its mouth to dissolve along with the female’s skin, which fuses the two together. Over time their bloodstream becomes one, and the male loses his eyes along with all other internal organs except for its testes. The female is now for all intents and purposes a hermaphrodite, meaning it can self-fertilize. A female may have more than six males on its body at one time. However, some females live their entire lives—which may span between 25 and 30 years—without ever encountering a male.

When the female is ready to reproduce, it lays eggs in a huge swath one meter wide by nine meters long. This sheet of eggs floats freely in the ocean’s waters. Larvae hatch from the eggs and feed on plankton at the water’s surface before returning to the ocean’s depths as they mature, beginning their unusual deep-sea life cycle once again.

More to Explore

• Anglerfish Lophius piscatorius
• Monterey Bay Aquarium: Fanfin anglerfish
• Deep sea anglerfish
• In-Situ Observations of a Deep-sea Ceratioid Anglerfish of the Genus Oneirodes (Lophiiformes: Oneirodidae) [pdf]
• Deep Sea Anglerfish

Last updated February 27, 2011 | Comments (7) | Permalink | Strange Biology