A video recording of a female anglerfish attached to her mate created a wave of excitement among marine biologists. Anglerfish have a quite striking look for most people. This deep-sea adapted fish is well known by the public with their scary huge teeth and a light emitting lure. There are about 160 species of anglerfish worldwide.
Most of what we know about these fishes have almost invariably came from dead specimens. Nobody has ever observed these animals in their natural habitat live.
This observation from the waters around Portugal’s Azores islands is so very precious for that reason. The almost fist-size female anglerfish can be seen with a dwarf male fused to her underside. Sexual dimorphism in anglerfish has reached extremes. For instance, males of the anglerfish species Photocorynus spiniceps is arguably the world’s tiniest vertebrate. Similarly, in the species Ceratias holboelli females may be more than 60 times longer and half a million times heavier than males.
Males have been reduced to almost parasitic way of life having no other function than a permanently attached sperm pouch. This could be a safe strategy in such dark environments where a female can consume the male just like other fishes triggering her lure. External fertilization requires mates to stay very close and release their eggs and sperms synchronously.
The biology behind sexual parasitism gets even more strange. It appears both sexes had to tone down and get rid of their innate immune systems for this bodily fusion to happen. Tissue rejection is a widespread phenomenon in vertebrates. Thus anglerfish apparently solved this physiological incompatibility problem by eliminating its adaptive immune system genes.
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