|Fish have been marked, using a variety of methods, for well over two hundred years. The first marks were simple external tags, such as wires or ribbons. In recent years, more advanced methods of externally marking fish have included branding, tattooing, and optical pattern recognition. Internal tags or marks have also evolved considerably in recent years, and now include both artificial as well as natural marks. Artificial marks include implanted wire tags, dyes on otoliths ("ear bones") or other hard parts, visible implants, and radio and ultrasonic implants. Natural internal marks include genetic marks, chemical / elemental marks, and biological marks (e.g., unique parasites, others). All of these various methods are used extensively, and each has unique advantages that are dependent on the goals of the marking program.
Marking programs are implemented for a variety of reasons, including estimating fish growth, mortality, exploitation, and movement. Angler cooperation is an essential component of these programs, and successful fish marking programs will result in more abundant and healthier fish for the sport fishery.