The Mating Story of Anglerfish

You ever heard of relationships where a partner is too dependent on his significant other? Perhaps it's good to learn a lesson or two from deep-sea anglerfishes.

When the anglerfishes were discovered, described, and classified in the 19th century, the specimens that they were working with were all females. They had no idea what the males looked like.

Some researchers occasionally found some other fish that are closely related to the female's body structure, but the distinguishing features like the scary maw and the lures were missing. It was significantly smaller as well: with lengths ranging from 6 to 7 millimeters in length. These creatures were classified into different taxonomic groups.

In 1922, Icelandic biologist Bjarni Saemundsson found a female anglerfish with two smaller fishes attached to her belly by their snouts. The biologist was puzzled by the arrangement but assumed that it was a mother and her babies.

Fast forward in 1924, Charles Tate Regan of the British Museum of Natural History found that the "babies" that they assumed was not the female anglerfish's baby nor a separate species of fish: it was her mate.

The male anglerfish that they had been looking for had been there are along: unrecognized and misclassified. The scientists eventually figured out the major difference between the male and the female: males do not have lures, or big mouths and teeth because they do not hunt, and they do not have to do so because the females do it for them.

Male anglerfishes, as simply put, are parasites of female anglerfishes.

To look for a mate, the male ceratoid follows a species-specific pheromone to the female, in which the lights from the female's bioluminescent lure will guide them to their potential mate. The males have a highly tuned sense of smell that leads them to the female pheromones.

When the male finds his mate, he bites into her belly and attaches into it until the two fishes become one. Skins, blood vessels are joined together, enabling the male to get all the nutrients necessary for his survival from his mate's blood. Males also grow much bigger after attaching, more significant than the free-swimming male ceratoid anglerfish.

With the male attached to his mate, he does not need to swim or eat as a typical fish does. Eventually, the body parts that he does not need: the eyes, fins, some internal organs atrophy, degenerate, and wither away. He takes food from her and provides her sperm when she is ready to spawn.

This weird mating ritual is necessary for deep-sea corticoids as they rarely find each other in the abyss, and to ensure the creation of little anglerfishes.

Females are not able to choose their mate. Some species of anglerfish, such as the Cryptopsaras, can host up to eight parasitic males.

Surprisingly, the mates release sperm and eggs into the water simultaneously during fertilization, even for females with multiple partners. Hormonal communication makes the release of sperm and eggs synchronized.

This peculiar mating ritual is not found in all anglerfishes. In some orders, males swim freely and hunt by themselves their entire lives. They only attach themselves to a female temporarily to procreate and then move on with their lives.