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0 <br /> <br />Tagging <br />Prior to stocking in areas of the upper Colorado River, fish will receive <br />a uniquely-coded PIT tag. Razorback sucker progeny could be PIT tagged at the <br />hatchery when they reach 75 to 100 mm total length (Burdick and Hamman 1992). <br />Marking hatchery-reared fish is necessary to 1) distinguish the various family <br />lots produced from paired matings of wild broodstock, 2) distinguish them from <br />wild fish, and 3) determine survival and movement patterns of stocked fish. <br />Size of Fish To Stock <br />Initially, either large juvenile (250 to 300 mm total length) or adult <br />D <br />razorback sucker will be stocked in the upper Colorado River. Stocking <br />razorback sucker this size may be more practical than stocking smaller <br />juvenile-size fish for the following reasons: <br />1. The habitat needs of wild young and juvenile razorback sucker in <br />the wild are largely unknown because they have rarely been <br />encountered by investigators. Therefore, until we have learned <br />D <br />what limits survival of young, stocking small juvenile fish is not <br />prudent. <br />2. Larger fish should have lower mortality rates than smaller fish <br />0 <br />following stocking. Large juvenile or adult fish would presumably <br />be immune to most predators, thereby enhancing survival and chances <br />for reestablishing a resident population. If smaller juvenile fish <br />are released into the riverine environment, survival would probably <br />be much lower, therefore requiring a greater number of fish to <br />achieve the same goals. Moreover, stocking success of juvenile <br />fish released into the river could not be evaluated for several <br />years until the fish had time to mature. <br />29 <br />0