During this period, females swell with eggs. Fully gravid females look as though they will burst, and the outline of the individual eggs may be seen through the tightly stretched abdominal wall. Males seldom leave their burrows, but will swim out several inches to meet a female. Occasionally, males will bite a female's fins, or even take a female's head entirely into their mouths. This does not appear to injure the female, though.
Male sculpins remain at their nest after breeding.
They fan their eggs, aerating them and keeping them free of silt. They defend their eggs against invertebrate predators and against their cannibalistic neighbors, and occasionally eat some of their own eggs. While the significance of this parental cannibalism is debatable, it does occur both in the wild and in captivity. Females breed only once per year but males are polygamous, and may mate with more than a dozen females during a single season. After about three weeks of development, the eggs hatch and the fry drop to the bottom of the nest.