Fish in the dark still size up mates

Female fish living in a cave still prefer a mate with a nice, big body, even though it’s too dark to see him.

In plenty of species, females choose large males, so that preference in the Atlantic molly (Poecilia mexicana) comes as no surprise.

What interested Martin Plath of Hamburg University in Germany and his colleagues was what happens when mollies adapt to life in a pitch-black cave.