A male tilapia's idea of a great chat-up line is to lose control of his bladder. Whether the object of his affections finds this chemical courtship appealing is questionable. But how does a male decide which lady to woo? Peter Hubbard and his colleagues at the Universidade do Algarve in Portugal suspected that male tilapia sniff out which females are about to spawn (p. 2037).

The group decided to test whether males can tell the difference between scents from pre-ovulatory females (those about to spawn) and post-ovulatory females (those that have already spawned). To see if body fluids from different females titillated males' olfactory receptors, they trickled water containing urine and faeces from pre- and post-ovulatory females past males' olfactory epithelia. Watching electro-olfactograms produced from the recordings of electrodes placed inside males' nostrils, they saw that males clearly find a whiff of pre-ovulatory female much more exciting than that of a post-ovulatory fish. The group suggests that pre-ovulatory females release some indicator of their sex appeal in their body fluids, while post-ovulatory females don't.

But do male tilapia also court pre-ovulatory females more enthusiastically? To find out, the group placed females in the males' tanks and kept a close eye on the males' behaviour. Sure enough, pre-ovulatory females found themselves fending off ardently urinating suitors, while post-ovulatory females didn't entice males to empty their bladders. So, female tilapia release sex pheromones to announce to their admirers that they're ready to spawn, and males passionately respond with their own chemical broadcast.