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1 1 1 1 1 I t 1 The design protocol for establishing test groups varied among the fish species tested and between the field and laboratory studies. This was because 1) the number of fish available between species differed, and 2) there were two different length classes of Colorado squawfish. For adult roundtail chub, juvenile razorback sucker, and the larger juvenile Colorado squawfish (225-300 mm TL), two test groups and a control group (no PIT tag) were established. The control and two test groups consisted of 20 fish each for Colorado squawfish and 25 fish each for roundtail chub. The test groups consisted of 1) a PIT tag implanted in the body cavity, and 2) a PIT tag implanted in the dorsal musculature. Because of limited availability, the number of fish per group for razorback sucker was less. At Gardner Pond, a control and two test groups were established; at Humphrey Pond, a control and only one test group were established. Smaller juvenile Colorado squawfish (120-165 mm TL) held at Hotchkiss NFH and Grand Junction consisted of a control group (no PIT tag) and one test group PIT tagged in the body cavity. For this study, we generally followed the guidelines and techniques for PIT-tag t t r 1 implantation developed for Pacific salmon (Prentice et al. 1987). We utilized a new version of the PIT tag (11 mm long by 2.1 mm in diameter; weight < 0.05 g) that was glass-encapsulated (the original was encapsulated in polypropylene). Only functional PIT tags were used. All fish, including the control group, were anesthetized with tricaine methanesulfonate (MS-222) prior to handling and tagging. The tag was implanted manually in test fish with a modified hypodermic syringe and 12-gauge needle. For juvenile (> 200 mm) and adult-size fish, the insertion location into the body cavity was 9