Across social media in the last week, there has been footage and compilations of a female anglerfish who, in her last few days alive, swam from the depths of the ocean to the surface just off the coast of California. The rhetoric on social media surrounding this 9cm anglerfish, belonging to the species Melanocetus johnsonii (with the first part meaning “black sea monster”), is that she wanted to see the sun and feel its warmth before she passed away. However, is there another reason she decided to make the journey to the surface of the ocean?
Anglerfish live in the most inhospitable habitat on our planet—the lightless depths of the sea. They primarily live at the bottom of the Atlantic and Antarctic oceans, although some live in more shallow, and tropical environments. Anglerfish can range in size, with some reaching up to four feet in length, so Melanocetus, being only 9cm, is really quite tiny. Anglerfish are very recognisable for a piece of their dorsal spine that protrudes over their mouth; although, it is only the female angler fish that has this feature. At the tip of the dorsal spine, there is a round piece of flesh lit by bioluminescence that is used to attract their prey.
Once their prey has been lured towards them by the luminosity, the large mouths of these fish can swallow a creature that is up to twice their own size.
This sighting of the anglerfish at the ocean’s surface is incredibly rare, having only been witnessed a few times previously, and has baffled biologists. Usually, these fish will be sedentary animals, only moving to ambush their prey, and yet this female actively swam to the surface of the ocean. One theory as to why she rose is that she consumed a fish that had a “swim bladder” or “gas gland”. This could mean that the gas then expanded inside her, lifting her to the ocean’s surface. The second theory is that she got caught in a warm water column, created from volcanic activity in the area. This, again, would cause her to be lifted to the surface against her will. Biologists and scientists can’t know for sure if either of these theories are correct; however, this sighting has helped to give them a better understanding of anglerfish and their biology.