The salmon were the first of about 6,000 in the American River expected to swim into the hatchery this year to spawn.
Laura Drath with the California Department of Fish and Wildlife says about 700 salmon will be allowed into the hatchery by department technicians at one time.
"They'll go through the fish and see if the females' eggs are ripe. If they are, they'll remove those eggs, the milk from the males, and fertilize the eggs and start them incubating. Fish that aren't ready to spawn yet will be put back outside into holding tanks and then checked again in several days."
About seven million eggs will be harvested and about four million fingerlings will be released back into the river in the spring.