The Astonishing Tale of Male Ceratioid Anglerfish and Their Permanent Fusion in Reproduction

Do you know how fish reproduce? Yes, in normal fish reproduction, male fish will produce sperms and female fish will produce eggs, they will remain separated individuals after the process of reproduction. However, deep sea ceratioid angler fish will permanently fuse with the female fish after reproduction! How is that possible?

Ceratioid anglerfish have extreme dimorphism, which means there is very large difference between male and female in the same species. Male ceratioid anglerfish are dwarfed and females are gigantic. In their reproduction, male ceratioid anglerfish has a set of pincher-like denticles at the anterior tips of the jaws for grasping and attaching fast to a female angler fish. In some forms, attachment is followed by fusion of epidermal tissues and uniting the circulatory system between the male and female angler fish, male become dependent on female for blood transported nutrients and female became self-fertilizing hermaphroditic host.

Now, let's think about why does patient who need transplantation of organs so difficult in modern medicine? Why can't we transplant any organ from a dead person to cure the person who is terminally ill? This is because our immune system have the function to reject any foreign pathogens to protect ourselves. Then how is this "fusion" reproductive way possible for ceratioid anglerfish? This sexual parasitism was enabled by their degeneration of adaptive immunity. Ceratioid anglerfish's molecular receptor has degenerated, lead to losses in critical aspects of the adaptive immune response such as V(D)J recombination, the ability to generate high affinity antibodies, T and B cell development, and antigen display. (Which do appear in human). This degeneration of immune system enables their unusual mode of reproduction.

Reference

Brownstein, C., Zapfe, K., Lott, S., Harrington, R. C., Ghezelayagh, A., Dornburg, A., & Near, T. J. (2024). Reproductive innovation enabled radiation in the deep sea during an ecological crisis. BioRxiv (Cold Spring Harbor Laboratory). https://doi.org/10.1101/2024.01.12.575380

Cassella, C. (n.d.). Anglerfish Physically Fuse to Their Mates, And We Finally Know How The Hell That’s Possible. ScienceAlert. https://www.sciencealert.com/anglerfish-become-physically-fused-to-their-mates-and-we-finally-know-how-they-do-it

Pietsch, T. W. (1976). Dimorphism, Parasitism and Sex: Reproductive Strategies among Deepsea Ceratioid Anglerfishes. Copeia, 1976(4), 781. https://doi.org/10.2307/1443462