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Decimal Coded Wire Tag™ (DCWT)

Product Information

The DCWT is a tiny length of magnetized stainless steel wire usually 1.1 mm long x 0.25 mm diameter. For very small animals tags half this length are used, and for larger specimens tags half again or double length may be utilized. These tags are marked with rows of laser-etched numbers denoting specific batch or individual codes. Single tags are cut from rolls of wire by a device/injector that hypodermically implants them into suitable tissue. Salmonid fishes are usually tagged in the snout, but "cheek" muscle and certain other tissue offers superior sites for many other species.

The decimal coding (etching) allows for either batch or individual identification. Batch codes, identifying a group of animals sharing one or more characteristics, are most commonly used for fisheries management purposes. Standard DCWT have batch coding; the same code is repeated over a specific length of wire. Sequential DCWT are designed to identify individuals or small groups; the code advances over a specific length of wire. The use of these sequential tags is somewhat more complex in requiring the saving or "archiving" of a DCWT before and after the implanted tag or tags.

DCWT are injected into tissue using automatic tag injectors (Figure 1), capable of implanting up to 1000 tags/hour; semi-automatic injectors achieving rates of several hundred tags per hour; or by using a single shot "muzzle loaded" syringe (useful for only small numbers of specimens and requiring pre-cut/magnetized tags).

Due to their small size, and usual position in opaque tissue, DCWT must be located and recovered using specialized magnetic detectors that come in various forms (e.g., Wand, tunnels, Portable detectors). Once excised, DCWT are visually decoded under magnification of about 10x. DCWT are normally dissected from dead/harvested fish, but the method offers considerable opportunity to recover data from living specimens as well:

Simply knowing a fish is tagged, as determined by the DCWT detector, can provide a simple "yes or no" answer (e.g., identifying hatchery origin fish in a mixed population, etc.).

Specific location (e.g., left cheek, right cheek, nape, origin of dorsal fin, etc.) of the implanted DCWT, as determined by a Wand Detector, can provide a number - increasing with animal size - of different "codes" (Tipping and Heinricher, 1993).

Shallow, and often visible implants of DCWT, may be excised without significant damage to the animal (Oven and Blankenship 1993).

NM has yet to encounter a fish, of sufficient size, that cannot be tagged. Arctic char Salvelinus alpinus as small as 22 mm total length have been successfully snout-tagged with "half-length" DCWT (). Since body muscle also provides a suitable and much larger target than the snout of a char, it appears that smaller fish and other organisms can be successfully tagged. Although designed originally for small fish, coded wire tags have been applied successfully in a number of crustacean studies.　

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