March, 1999

Mass marking is a technique used to distinguish hatchery-produced chinook and coho salmon from wild fish.

Marking offers fishers an obvious way to tell if their catch is a hatchery fish which may be kept, or a wild salmon which must be returned to the water. Marking allows fishing to continue on hatchery stocks, while protecting wild fish in waters where the two stocks intermingle.

Hatchery fish are marked by removal of their adipose fin, a small fin on the fish’s back near the tail.

Mass marking has been used by the Department of Fish and Wildlife since 1996.

Until recently, all marking was done by hand. To mark a larger number of fish, the Department of Fish and Wildlife is beginning to use an automated fish marking system. The new mass marking machine is housed in a trailer which can be moved from one hatchery to another when marking is underway.

The marking machine, which can mark 7,000 fingerlings per hour, or two fish per second, uses a flow of cold water to attract fish to a chute where mechanized gates separate them and hold them for individual fin clipping. A tiny camera and special software helps position the clipper and verifies that the adipose fin is removed.