Female ocellated wrasses prefer males that build nests and take care of the fertilized eggs as they develop. In this video, a male and female spawn in the nest. Other types of males do not provide parental care and compete to fertilize the eggs. Small "sneaker" males hang out around a nest and dart in to release large amounts of sperm when a female is spawning. The females, however, seem to have found a way to thwart the sneaker males by giving an advantage to the nesting male's sperm. A new study shows that ovarian fluid released with the eggs during spawning favors sperm from the nesting males, limiting fertilization by sneaker males.