Parents and Sneakers

Midshipman fish have two classes of reproductively active males known as parental males and sneaker males. Parental males build and guard nests from intruders and mate call ("hum") to attract females to their nests. Sneaker males neither build nests nor mate call, but instead they sneak into a nest and try to steal fertilizations from the parental male when a female is present. Shown here is (top to bottom) a sneaker male, female, parental male, and sneaker male. Also, shown near the bottom are newly hatched embryos.