For Mates to Fuse Bodies, Some Anglerfish Have Lost Immune Genes

In most vertebrates, the absence of adaptive immunity would be catastrophic, but in some deep-sea angler fish species, it enables their “wild” and “wacky” mating habits.

katya katarina zimmer
| 6 min read
deep-sea anglerfish Melanocetus johnsonii mating parasitic male immunology adaptive immune system cytotoxic t cell antibody

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ABOVE: A 75-mm-long Melanocetus johnsonii female with a 23.5-mm-long male attached to her belly
EDITH A. WIDDER

Krøyer’s deep-sea anglerfish, Ceratias holboelli, does not spawn, copulate, or do anything a fish would ordinarily do to mate. Instead, the male—just a few inches long—clasps onto the comparatively gigantic female’s body and never lets go. Slowly, his body morphs into hers, his cells becoming hers, including his testicles, which are used to make offspring. As he vanishes, two individuals become one—taking the concept of monogamy to a new level.

The sub-order of deep-sea anglerfish, composed of nearly 170 known species, arguably displays the most dramatic mating habits in the animal kingdom. In some species, males only temporarily attach to females and then part ways. In others, such as C. holboelli, males permanently “fuse” with females, or females absorb multiple males—in some cases up to eight at a time.

Among the many mysteries surrounding ...

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Meet the Author

  • katya katarina zimmer

    Katarina Zimmer

    After a year teaching an algorithm to differentiate between the echolocation calls of different bat species, Katarina decided she was simply too greedy to focus on one field. Following an internship with The Scientist in 2017, she has been happily freelancing for a number of publications, covering everything from climate change to oncology.
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