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304 were individual (usually five) rather than the continuous suture used by Bidgood, and the incision was made laterally, immediately anterior and slightly dorsal to the insertion of the right pelvic fin. Implanted fish were held five days in 1980 in order to determine the results of the surgery. Thereafter, the fish were released after implanting them in order to reduce stress associated with holding them (Hart and Summerfelt 1975). Surgical implantation was completed with AVM company and Smith- Root Company fish transmitter modules dipped in melted beeswax. Four different modules were used that varied in weight from 10 to 23 g in air and about 3.5 to 6 g in water. The units are powered by mercury bat- teries and had a life from 6 to 18 months, depending on the model used. All units transmitted in the 40.660-40.700 MHz frequency range. Each transmitter had a unique signal (frequency vs pulse rate) so that individual fish could be identified.. Radio receiver sets used were Smith-Root RF-40 and SR-40 models. The RF type enabled the investigator to identify any particular frequency transmitted at 40 MHz. The SR receiver was a "search" type and received all emitted frequencies in the frequency range. Omnidirectional and pin-pointing type (bidirectional) antennas were employed. A Larson-Kulrod whip antenna was used to search for implanted fish. This antenna was mounted on a 20 cm square steel plate elevated about 4 m above the water when mounted on a boat, or mounted directly to an airplane, or helicopter strut. A Smith-Root loop antenna (directional) was used only to triangulate fish location, from boat or shore. RESULTS AND DISCUSSION Two spawning migrations were identified in the Green River Basin by tracking 23 radioimplanted Colorado squawfish. One migration, iden- tified in 1981 (Figure 1) was reconfirmed in 1983 (Figure 2). A total of i4 Colorado squawfish migrated downstream and two migrated upstream to spawn in the lower 30 km of Yampa Canyon. Another migration, sus- pected in 1981 was confirmed by 1983 after 7 Colorado squawfish were followed to the same general area in Gray Canyon of the Green River (Figure 3). Collections made at the Yampa site in 1983 produced two Colorado squawfish tagged there in 1981 and 1982, demonstrating a fidelity to the spawning grounds. Potamodromous migrations (Myers 1949) of North American riverine fishes have received little study in comparison with the information developed for anadromous forms. Until now, homing - a regular movement