The fish with its genitals on its head

The male fish, a Phallostethus cuulong just 2 centimetres long, weaves between drifting vegetation in the sluggish waters of a canal. He closes in on a female, swims alongside her and tries to mate with her. But to an outside observer, he seems to be doing it wrong. His head is right next to the female's, but he's at a 45-degree angle so his rear end is well below hers. Sounds misguided, but actually he's doing it exactly right – it's just that his gonads are on his head. This is the challenge faced by all priapiumfish, a little-known group of Asian fish that have their reproductive organs on their chins, just behind their mouths.
 How does this Cronenbergian arrangement work?