Coded wire tag

The tag is marked with rows of numbers denoting specific batch or individual codes.

The CWT is not visible once inside the fish; its presence is detected at close range by using a handheld wand or tunnel type detector that can sense the magnetized metal.

Upon insertion, information about the fish such as hatching date, release date, location, species, sex, and length are recorded along with the corresponding tag code into a database, so that codes on recovered tags can be matched to information within that database.

[1] With advancements in laser technology, digits could be etched on tags, which caused the switch from binary to decimal codes.

[6] Coded wire tags are used to track groups or individual fish for research and fishery management purposes.

Commonly tagged species are coho, chinook, steelhead, chum, sockeye, and pink salmon.

However, in Washington the adipose fin is removed from nearly all hatchery salmon in mass marking programs to distinguish them from wild fish.