BRIEF: 'Sneaky' Male Fish Not As Sly As They Might Think

It's all thanks to the ovarian fluid.

Some male ocellated wrasse build seaweed nests to attract females. The fish are found in the eastern Atlantic and throughout the Mediterranean Sea. 

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Courtesy of Susan Marsh-Rollo

Emily DeMarco, Staff Writer

When it comes to sex, some male fish can't catch a break. In species such as the ocellated wrasse, females prefer to mate with "nesting" males that build handsome seaweed nests, court females and care for eggs over smaller, less colorful "sneaker" males. Forgoing any courtship or paternal duties, these males instead wait for a female to release her eggs near a nesting male before sneaking up and inundating the nest with large numbers of sperm. To counter, nesting males release fewer but faster sperm. Scientists have thought that in this fish species and in others the two types of sperm competed to fertilize the eggs, with the outcome completely out of the female's fins. Now, a new study, which was published today in Nature Communications, finds that ocellated wrasse females hold more sway than researchers realized. Their experiments reveal that the ovarian fluid females release with the eggs creates conditions that increase the speed and accuracy of sperm moving toward the eggs. That favors the already swift swimmers of the nesting males, frustrating the sneaker males and their sperm. Who runs the world? As Beyoncé and these female fish know, it's clearly the girls.

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Emily DeMarco is a former Inside Science staff writer. Follow her on Twitter: @emily_p_demarco