Because angler fish are so sparsely populated throughout the vast
millions of cubic miles of ocean, chance mating encounters between
males and females would be unlikely. In fact, when deep-sea anglers
were first brought up in trawls they puzzled scientists because they
were all females. Then someone noticed small “growths” on the female
that turned out to be males.
When a tiny male meets a female he bits
into her flesh and literally fuses with her body. Like the linking
together of web sites on the Internet, the two blood supplies also fuse
together so that the male obtains nutrients and oxygen from the female.
Without any need for most of his organ systems, such as eyes and
digestive organs, the male’s body degenerates into essentially a pair
of sperm-producing testicles. Thus the female essentially becomes a
hermaphrodite with up to six or more of these tiny male parasites
attached to various parts of her body.
Although functionally bisexual,
the eggs and sperm come from genetically distinct parents, thus
providing vital genetic variability through meiosis and genetic
recombination. As a functional hermaphrodite she can have sex any time
or place, without worrying about meeting a male in the dark abyss of
the ocean. Clinging to her body like minute, blood-sucking parasites,
the males have little interaction with the female, except to fertilize
her eggs with sperm.