A wild fish, below, has an intact
the adipose fin has been
removed from a marked fish, above.
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.