8 Things You Probably Didn't Know About the Seadevil Anglerfish
By now, you've probably seen the awesome footage of a Black Seadevil anglerfish captured by scientists with the Monterey Bay Aquarium Research Institute (if not, you can watch it above). The video, shot at 1900 feet below the surface by a remotely operated vehicle, is believed to be the first footage of a live Seadevil in its natural habitat. Because the creatures live at such great depths, they're rarely seen alive—and, because of that, we don't know a whole lot about them. We asked John Sparks, a curator in the American Museum of Natural History's Department of Ichthyology, to tell us a few things scientists do know about this weird fish.
1. There are six species in the Melanocetidae, or Black Seadevil, family. This one is a female, "probably the Humpback Anglerfish," Sparks says. The fish was first described by Albert Günther, keeper of zoology at the British Museum in London, in 1864. He had obtained it from English naturalist James Yates Johnson, who had gotten the fish from Madeira [PDF]—hence its scientific name, Melanocetus johnsonii.
2. You may have heard how some anglerfish reproduce via the males fusing their bodies to the females' until they essentially become one; the male loses his eyes, fins, teeth, and some internal organs and, from that point forward, lives off of the female, providing sperm when she's ready to spawn. Those fish "are members of the suborder Ceratioidei, [or] deep sea anglerfishes, in which some species are known to reproduce by that means," Sparks says. Still, that's not the norm for those fish—scientists have so far only found parasitic males in 5 of 11 ceratioid families, according to Sparks—and it's probably not what happens when humpback anglerfish mate, either. "That has not been found—yet—in this species," Sparks says. "In the family this species belongs to, only loosely attached, non-parasitic, males have been found on females—they still retain their teeth, etc."
3. The females are much bigger than the males. Typically, Sparks says, this species is "3 to 3 1/2 inches [long]. The largest male known is under 3 centimeters (1.18 inches), whereas the largest female is 18 centimeters (7.08 inches)."
A sketch of the Humpback Anglerfish from the 1896 book Oceanic ichthyology : a treatise on the deep-sea and pelagic fishes of the world, based chiefly upon the collections made by the steamers "Blake," "Albatross," and "Fishhawk" in the northwestern Atlantic. Photo courtesy the Biodiversity Library on Flickr.
4. The tip of the pole-looking thing protruding from the fish's head is called the esca, and its bioluminescence is produced by symbiotic bacteria. This is key in getting the anglerfish fed, because it isn't built for giving chase. "[It's] just swimming slowly, as their body shape—globular—dictates," Sparks says. So in dark environments, the fish uses the glowing esca, which it can move to emulate prey, to attract its own prey, and—in a classic case of the hunter becoming the hunted—chomps down on whatever gets too close...
5. ... with those crazy-looking teeth. "They are sharp and [are] used to impale prey items," Sparks says. "They have large mouths and can eat quite large prey items." Günther, in his description of Melanocetus johnsonii, notes that
The gape is enormous; and although the lower jaw is vertical when the mouth is closed, it can be moved downwards at more than a right angle ... the prey which can be received within the cavity of the mouth actually may exceed the size of the fish itself.
When the specimen was brought to him, Günther said, "the belly was much distended, and contained, rolled up spirally into a ball, a Scopeline fish, which measured 7 1/2 inches in length, and 1 inch in depth."
6. The video mentions the dots on the anglerfish's face, which are organs that allow it to sense movement in the water. These, Sparks says, are called neuromasts, and they're "part of the lateral line system. Agnathans, or jawless fishes, up through amphibians have them. They are for sensing pressure (water movement)—in some species, such as cavefishes, they are quite numerous and well developed."
7. AMNH has the Humpback Anglerfish in its Ichthyology collection. "It's probably the most commonly captured member of Melanocetidae," Sparks says. "It has a wide distribution and is found in all oceans."
8. Though this probably wasn't the anglerfish seen in Finding Nemo—"If I remember correctly the 'species' depicted in Nemo was far more elongate; [it] seemed to me to be an amalgam of different species," Sparks says—the humpback anglerfish is still a star: It once appeared on the cover of Time.