anglerfish

The deletion of genes related to immune response has no-doubt been invaluable for anglerfish, since the female’s body would otherwise likely reject the foreign tissue of her attached mates.

Researchers found that anglerfish species that go for the most permanent, multi-partnered version of this mating routine have basically no ability to mount an attack against a novel infection.

For deep-sea anglerfishes, sex resembles an organ transplant.