It is a sea creature which, it seems, does not need to rely on good looks to attract a mate - which is perhaps just as well.
The sea lamprey - a parasitic, eel-like fish native to the north Atlantic - is a notoriously unusual looking beast.
Now scientists have discovered something else unique about this ancient animal of the deep: the male attracts a partner by using its semen as an aphrodisiac.
A powerful, odorous pheromone released from the fluid makes it irresistible to nearby ovulating females – who will arrive at the male’s nest ready and eager to copulate.
It is the first time semen has been found to have such an effect in the animal kingdom, researchers say.
The discovery, by scientists working together at Michigan State University in the US and Shanghai Ocean University in China, is published on Wednesday in the open-access journal PLOS Biology.
"We found the semen of sea lamprey contains spermine, a highly specific and potent pheromone, which attracts only ready-to-mate female sea lampreys," said lead researcher Anne Scott. "This discovery implicates a new strategy that male animals use to recruit mates through the release of chemical cues in semen.
“Ovulatory females likely use the spermine released along with sperm as a reliable signal for the presence of actively spawning males in the vicinity."
The chemical does not appeal to either males or pre-ovulatory females, she added: researchers identified the specific spermine-activated receptor in lamprey olfactory tissue, and a compound that blocks this receptor prevented the attraction of ovulatory females.
Although the lamprey itself is a sea-dwelling creature it can be seen in British rivers where they swim, salmon-like upstream, to breed in shallow waters. They feed by attaching their fierce teeth to other fish and sucking the blood - and eventually life - out of them.
The new discovery, the article suggests, could have management implications for either the control or conservation of sea lamprey populations.
