Who's the daddy? Female fish have novel way of finding reliable mates

Ocellated wrasse are able to influence which male fish fertilise their eggs, helping to sort stable nest-makers from the ‘dead-beat daddies’ of the fish world

Nicola Davis

Tuesday 16 August 201617.39 BST Last modified on Tuesday 16 August 201617.59 BST

Female fish have a novel way of finding Mr Right when it comes to picking fathers for their offspring, scientists have revealed.

Like most other species of fish, female ocellated wrasse release their eggs into the water for fertilisation by males, making just who ends up as the daddy something of a lottery.

But now researchers have revealed that females are able to influence which males will succeed in fertilising their eggs.

While a number of species that rely on internal fertilisation boast such mechanisms, including the duck, the new finding is a rare example of this ability being found in a species that undergoes external fertilisation.

Writing in the journal Nature Communications, a team of researchers from the US say that the female ocellated wrasse is able to sort Mr Nice from Mr Nasty thanks to a substance, known as ovarian fluid, that coats the eggs she has released.

The preferred type of mate is the nest-building male who guards offspring and woos females. By contrast, males which shoot sperm at the eggs and flee – so-called “sneaker males”– are less favoured. “They are like the dead-beat daddy of the fish world,” says Kelly Stiver, co-author of the study from Southern Connecticut State University.

But while nesting males produce sperm that swim faster than that of sneaker males, there is a hitch. Sneaker males release more sperm.

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