Sexual Parasitism in Deep Sea Anglerfish
In response to the perilous and opportunistic conditions of the deep sea, some deep sea anglerfish have evolved a very specialised method of reproduction - sexual parasitism.
Due to the fact that individuals of a species are locally rare, encounters between a male a female are very uncommon. As such, when they eventually meet, the fish employ a unique mating method that will ensure that they never separate again.
The fish display extreme sexual dimorphism, with males being many times smaller than females. The method by which a male finds a female differs across different species, but can involve sight or pheromone cues.
When a male anglerfish encounters a female, he latches onto her body with his mouth. He then releases enzymes that digests the skin of his mouth and her body, which fuses the pair down to the blood vessel level.
The male becomes a parasite, surviving solely on the nourishment provided by the female via their linked circulatory systems. In return, he provides sperm for the female. Eventually, his body atrophies until only the gonads are left.
Sexual parasitism benefits both the males and females. For the females, it ensures that there is an immediate source of sperm as soon as she is ready to spawn. The males, being much smaller and less adapted for survive, are much more likely to sire offspring attached to a female than if they were to live a solitary life.
Image: © Pietsch, TW