A coded wire tag (CWT) is an animal tagging device, most often used for identifying batches of fish. It consists of a length of magnetized stainless steel wire 0.25 mm in diameter and typically 1.1 mm long. The tag is marked with rows of numbers denoting specific batch or individual codes. The tag is usually injected into the snout or cheek of a fish so that it may be tracked for research or fisheries management.
Fish, crustaceans, insects, gastropods, and many other animals have been successfully tagged with Coded Wire Tags. The coded wire tag program in the Pacific Northwest[1] has been described as the largest animal tagging program in history, with over 1 billion salmon tagged.