Strange Things Happen at Sea

The fish made famous by the film Finding Nemo. They're attractive little fish that have a special protective mucous enabling them to live safely amongst the arms of a large anemone that would sting other creatures to death.  Often living in small groups, the largest individual of which is female, the second largest being the dominant male, who regularly mates with the female. The other smaller fish are all male.

 

 

In the environment where these fish live (>1000m depth), food is relatively scarce so they have evolved a number of adaptations to deal with this.  For example, they have a luminous lure to attract prey, an elasticated stomach in order to be able to eat quite large items, and dwarf males. The male deep-sea anglers can be so small that in one species the male is a candidate for the smallest known fish in the world. The idea behind this is that as the male is producing sperm which are around a 1000th of the size of an egg, the male can still produce millions while being very small, and consequently he will need a lot less food to be able to do this.

 

But male anglers have taken this to such extremes that they cannot survive without a female, to which they attach themselves like little vampires and feed off her blood (the record being 7 males on one female). In some species they detach occasionally and go in search of another female but in others the attachment is permanent and in some cases the skin of the female grows over the male and he becomes little more than an organ making the female in effect a hermaphrodite.