As their name suggests, Mexican mollies (Poecilia sphenops) live in Mexico, being a fairly common species that resides in a range of habitats from small rivers to creeks and lakes.

The fish has a complicated mating behaviour, with males fertilising females internally, rather than spreading sperm over externally laid eggs.

Sexy company

Not all males are equal, however.
Some possess a moustache-type structure growing from scales on their top lip.

Until now, its function has not been known as it has not been studied or described in any detail.

So zoologist Professor Ingo Schlupp of the University of Oklahoma in Norman, US and colleagues in the US and Germany decided to study it for the first time.