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1 1 fl 1 u years (e. g., 1983) (Table 1). Figure b shows the relationships between discharge, water temperature, and migration period for 1981-1983. For each year, Colorado squawfish initiated spawning migrations 8-12 days following a spring peak flow of about 3.5 times the mean annual discharge and a river temperature regimen exceeding 11 C. It is not known whether these conditions are requisite for initiation of spawning movements, but we believe some combination of endogenous and exogenous factors are necessary (including temperature, discharge, photoperiod), and that neither discharge nor temperature alone are adequate for initiation of spawning migrations. .Effect of exogenous factors on the control of reproductive cycles of cyprinid fishes is well known (Bye 1984). Zt is possible that inputs of certain chemical substances due to spring flooding, in combination with increasing water temperatures, acts to initiate spawning migrations in Colorado squawfish. Homing behavior in Colorado squawfish is indicated by long distance 1 u w 1 movement patterns and repeated recaptures of the same fish on the Yampa River spawning ground in subsequent years (Tyus 1985, Wick et al. 1983). Of four fish radiotracked to the Yampa River spawning grounds for 1+ years, two migrated to the same location in consecutive years, indicating fidelity to the spawning site. Recaptures of fish on the Yampa River spawning ground also supports the concept of fidelity in Colorado squawfish. A total of five Colorado squawfish in breeding condition have been tagged and recaptured in the Yampa River between RM 11 and RM 18 for intervals of 1+ years (3 fish for two consecutive years, 1 fish after a two year interval, and 1 fish after a three year interval). Adult Colorado squawfish using the Yampa River spawning grounds have not been found to use any other spawning site throughout the Green River system. 13 1