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Species: Phallostethus cuulong
Habitat: surface waters of the Mekong River in Vietnam
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?
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Phallic fish
P. cuulong is only the 22nd known priapiumfish, which are named after the ancient Greek fertility deity, Priapus. They all belong to a family called Phallostethidae and live in south-east Asia.
The new species was discovered in July 2009 by Koichi Shibukawa of the Nagao Natural Environment Foundation in Tokyo, Japan. He saw one swimming alone in a canal near the Mekong River in Vietnam, and managed to catch it in a net. Working with colleagues at Can Tho University in Vietnam, he realised it was a new species.
Male priapiumfish don’t have a penis like humans and other mammals. Instead they have a unique organ called a priapium, which faces backwards and looks like a muscular nozzle. It’s actually a modification of the fish’s pectoral and pelvic fins.
The priapium of P. cuulong has two attachments, both of which look frankly dangerous. At the bottom near the tip, there is a forward-facing serrated saw, or ctenactinium. Further forward, right under the head, there is a forward-facing rod called the toxactinium.
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