Aug 29, 2012

A new species of fish discovered in Vietnam is only 2 centimeters long, but its tiny size is not the creature’s only unique trait. This fish possesses sexual organs in an unusual place: Its head.

Scientists do not yet understand the evolutionary origin of the unusual placement of the fish's reproductive system.

One theory posits that a “bilaterally asymmetric organ” under the throat is “for holding or clasping onto females and fertilizing their eggs internally.” The vast majority of fish species fertilize their eggs after they are laid.

The Phallostethus cuulong – the scientific name of the fish – has become the 22nd member of the Phallostethidae family, a group of small, slender and nearly transparent surface-swimming fish that live in the waters of southeast Asi. 

The new species was first discovered near the Mekong River in July 2009 by Japanese scientist Koichi Shibukawa. He managed to catch it in a net, and began researching it alongside colleagues from Vietnam’s Can Tho University.  

The discovery of a ‘penis-headed’ fish came less than a month after a biologist in the Amazon uncovered a species of extremely rare caecilian – a legless amphibian – that was also shockingly phallic in shape.

AFP Photo/Koichi Shibukawa, Tran Dac Dinh and Tran Xuan Loi

Photographed by L.X. Tran and K. Shibukawa

Photographed by L.X. Tran.