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Published on: Mar. 23, 2011

Lake Sturgeon

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Fin Cutting

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Scanning a Coded Wire Tag

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As kids, we enjoyed chasing friends in a game of tag. Now that we are a little older, and work as fisheries biologists, we are involved in a different version of tag. No, we aren’t chasing each other around one of the conservation areas. Rather, we’re tagging a variety of fish species to learn about the critters that swim in our big rivers, lakes and streams. And you, as anglers of Missouri, can help us.

Marks and Tags

There are a variety of ways that fisheries biologists can identify individual or groups of fish. In some cases, the easiest thing to do is to mark the fish. For instance, the Missouri Department of Conservation began stocking fingerling lake sturgeon into our big rivers in the 1980s. The first two batches of fish were marked by clipping off one of their pelvic fins. This permanent mark affects the fish for only a short time, but allows biologists to identify those fish for the rest of their lives. Several of the fish have been recaptured in the Missouri, Mississippi and Illinois rivers.

Occasionally, biologists will cut off a small piece of a fish’s fin to mark it temporarily. This short-term mark helps us estimate the number of fish in a population and has very little impact on the fish. Often, the piece of fin grows back.

The more common method of marking fish today is to use a variety of tags. Some of them are very simple, while others incorporate modern technology. A simple tag commonly used is called a coded wire tag, or CWT. This tag is a 2- to 3-millimeter-long piece of wire that is embedded somewhere in the fish’s flesh or fins. The only way to detect it is to use a very sensitive metal detector. Because biologists can’t see the tag, the tag’s location on the fish is the key to telling us which batch of fish it belongs with. This type of tag is frequently used to mark an entire batch of fish stocked in a given year.

A more advanced type of tag is the passive integrated transponder tag, or PIT tag. PIT tags used in Missouri are rarely more than 5 or 6 millimeters long. Each tag has a unique series of letters and numbers that help us identify each individual fish. A special reader sends a signal to the PIT tag. The signal charges the

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