Scientists have discovered a species of freshwater fish in the Mekong River in Vietnam in which the male has genitals on its head, according to a report on New Scientist magazine.
In a paper published in the journal Zootaxa on July 3, Koichi Shibukawa of the Nagao Natural Environment Foundation in Japan and Tran Dac Dinh and Tran Xuan Loi of Can Tho University's College of Aquaculture and Fisheries described a new species of priapiumfish.
The species was discovered in July 2009 by Shibukawa. He saw one swimming alone in a canal near the Mekong River in Vietnam, and managed to net it. Working with colleagues at the Can Tho University, he realized it was a new species.
The new species, named Phallostethus cuulong, belongs to the genus Phallostethus, while cuulong is the Vietnamese name of the Mekong.
The fish do not have a penis like humans and other mammals. They are equipped with a unique organ known as the priapium on the underside of their head, which is used for clasping a female while simultaneously entering the body cavity and fertilizing eggs internally. The female subsequently lays fully-fertilized eggs rather than giving birth to live young.
Phallostethus cuulong is only the 22nd known priapium fish, which are named after the ancient Greek god of fertility, Priapus. They belong to a family called Phallostethidae and live in southeast Asia.
The male Phallostethus cuulong is just 2 centimeters long.