Underneath that scary look is a fascinating world of science meshing with the reality of a deep-sea predator.
My first exposure to an anglerfish was in Finding Nemo when out of the blue a glowing light appeared behind Marlin and Dory, only for them to soon find out it was a hungry, monstrous anglerfish! Usually thought of as their characteristic appearance, including a protruding mouth lined with inward-facing transparent, sharp teeth, and their bioluminescent “fishing lure”, the anglerfish is a rare, fascinating species! Whether you’re overwhelmed with your own studies or simply like to learn new things, this article is a perfect way to reorient yourself into the massiveness and intricacies of our world, as well as some good back-pocket trivia knowledge. Come dive into the weird and amazing world of the anglerfish, specifically looking at their unique evolutionary adaptations acquired throughout the centuries.Â
Although I’ll be focusing more on the deep-sea anglerfish, there are more than 200 species of anglerfish, usually living in the murky depths of our global waters, most notably in the Atlantic and Antarctic oceans, where they are seen close to or away from the seafloor, depending on the species. The anglerfish diet is carnivorous, usually consisting of crustaceans and small fish, however, they can swallow prey (ex. squids, fish) twice their size with their extendible mouths and pliable body. Speaking of size, anglerfish range from 8-40 inches (from an average banana to a meter long) and can weigh up to 110 pounds, with females being significantly larger than males. According to the Fishes of the World (5th edition), anglerfishes are classified into five suborders, with a couple like the sea toads and batfishes being able to walk on the deep seafloor, with others like the monkfishes and frogfishes being able to camouflage amongst the sea floor.Â
Today, however, I want to talk about the recognizable deep-sea anglerfish in the last and biggest family: Ceratiodei. Due to their habitat being in the deep depths of the ocean, much is still unknown about the deep-sea anglerfish. However, there are a couple of evolutionary adaptations that scientists have discovered including their ways of predation and mating that are pretty unique to their species.Â
First, we will start off with their method of predation, titled ambush predation. Interestingly, only females are predatory, characterized by a modified, bendable dorsal spine resembling a fishing lure, or the illicium, with a bulb containing bacteria producing bioluminescent light, or the esca. Working in a symbiotic relationship (in which both species benefit), the bacteria create light through a chemical reaction involving luciferin, a light-emitting molecule, to help females find prey and mates, while the anglerfish provides protection and nutrition for the photo-bacteria in return. A muscular skin flap is used to hide or reveal its lighted lure, which is used in addition to moving the lure back and forth to attract prey. The way the bacteria finds its way into the female anglerfish’s esca is still undetermined, whether it’s something picked up as the anglerfish swims around or if it’s passed on by the mother earlier in development. However, one study has hypothesized and collected evidence to suggest that anglerfish actually collect such bacteria through direct contact in their environment, rather than it being passed on generationally.Â
Lastly (and in my opinion, the weirdest yet coolest evolutionary adaptation) is the deep-sea anglerfish’s way of mating, termed sexual parasitism. Considering the vastness and loneliness of the deep ocean, it’s no surprise that such dwelling species need to come up with unique mating routines due to the rarity of finding a mate. The mating process consists of the female laying a gelatinous sheet full of eggs followed by fertilization before being left to slowly float up to the mid-ocean region. Once birthed, the larvae feed on plankton before making their way back down to the deep sea. In a very simplified statement, the small male bites on to the larger female, with latching being temporary (letting go once the mating process has finished) or permanent, depending on the species.
Through obligate parasitism, the male permanently latches on to the female and their circulatory systems slowly fuse, leading to the male becoming nothing but a sperm-producing organ (like, DAMN)! Multiple traits are needed to adapt to make this form of mating possible, including the extreme sexual dimorphism represented in size and presence of a lure for predation as well as the need to shed their adaptive immunity in order for the female to not manifest a destructive immune response towards her fusing mate. Researchers are particularly interested in the anglerfish’s shedding of adaptive immunity to apply it to life-saving medical procedures such as organ transplants and skin grafting where immunosuppression is necessary for successful treatment.Â
The deep sea is thought to have as much (or more) biodiversity as tropical rainforests, consisting of possibly 10 million different species! Although it makes up 95% of the Earth’s living space, its extreme conditions have limited scientist’s access to the deep-sea world and have resulted in limited knowledge and research about such species. The deep sea is crucial for human life, as deep-sea currents drive global weather systems, fuel vital marine food chains, capture an abundant amount of carbon dioxide, and show promising results for the future of cancer, antibiotic, and viral research. As such, it’s important for the college generation to advocate for deep-sea biodiversity and to stand against climate change and ocean acidification as well as saying NO to deep-sea mining! Just as much advocacy towards conserving rainforests should also be put towards deep-sea biodiversity (even if the creatures look somewhat disturbing)!Â