Faking it? Chitose Yamazaki & Itsuro Koizumi

FAKE it ’til you make it. Female lampreys mate hundreds of times but secretly withhold their eggs until they are sure their suitor is worthy.

During the mating season, male and female Siberian brook lampreys (Lethenteron kessleri) meet for orgies in specially built nests in the streams where they live. Individual female fish appear to mate up to 200 times, with 10 or more different males.

Until now, the benefit of these marathons for female lampreys has been unclear, because they require lots of energy. Now Itsuro Koizumi at Hokkaido University in Japan and colleagues have found that in most sexual encounters, the female brook lampreys do not release eggs.


The would-be fathers appear not to notice when their female partners trick them by withholding their eggs, Koizumi says, as they still release clouds of sperm into the water.

Female lampreys were more likely to engage in sham mating when grouped with lots of males, hinting that they were pickier when they had more choice. This fits in with the idea that sham mating allows the females to select the father of their offspring.

Some female birds and mammals also mate with multiple males – a process known as cryptic choice. But this involves sperm selection once it is actually inside the female’s reproductive tract. Cryptic female choice in species where the eggs are fertilised outside the body has only been reported in a handful of animals.

Despite the mating marathons female lampreys may not choose the father of their offspring based on sexual prowess. Instead, it could be to do with how many stones males can move during nest building, Koizumi says.

Brook lampreys only grow eyes as adults, and the females have larger eyes than males – possibly because they need them to scope out the best mate (Journal of Ethology, doi.org/bzzp).

This article appeared in print under the headline “Fish fake egg release during prolonged sex”