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Ecological Significance of Colorado Squawfish Migration Long distance (over 100 km) spawning migrations in freshwater fish species is generally uncommon in North America. Nikolsky (1978) cites examples in Asia of cyprinid fishes that migrate over 1000 km. Other fishes of the genus Ptychocheilus include the northern squawfish, P. oregonensis) and the Sacramento squawfish (P. rag_ndis). These two squawfishes also make freshwater spawning migrations (Reid 1971, Moyle 1976). Regarding the family Cyprinidae, little is known about behavior in endemic cyprinids of the United States since they are not generally important for commercial and sports fisheries. Most emphasis has been placed upon anadromous (shad, salmon and striped bass) and catadromous (eel) forms. Virtually nothing has been learned about potomodromous (freshwater) riverine migrations. Certainly, such migrations occur among cyprinids, since some are well known in Europe and Asia (Stott et al. 1962, Nikolsky 1978. Because the family Cyprinidae is the largest family of fishes in the world, with 275 genera and over 1600 species (Nelson 1976), it is probable that a high degree of diversity and adaptation occurs in this family, possibly more than in any other. According to Northcote (1967) spawning migrations benefit fish species by insuring successful re- production, since the location of mates and appropriate spawning con- ditions would coincide. The deposition of eggs in an area with good downstream nursery areas is also important for stream spawners. The interrelation of upstream spawning sites and suitable downstream nursery areas is probably a significant key to the survival of the Colorado squawfish. Suitable spawning sites for Colorado squawfish appear limited in the Green River basin and the known or suspected sites appear to be far removed from suitable adult habitat and in some cases from nursery habitat. Water resource development in the Colorado River Basin probably blocked access to spawning sites and resulted in a loss of Colorado squawfish subpopulations. The exact origin of the North American native cyprinids is unknown; however, Darlington (1957) indicates they are immigrants from eastern Asia, arriving in North America in the Miocene epoch of the Tertiary. The mechanism appears to have been a dispersal via northern latitudes. The lake chub Couesius plumbeus) presently occurs throughout Canada and into the Arctic Circle where it undertakes stream spawning migrations (Scott and Crossman 1973). The development of spawning migrations in North American stream fishes may be linked to the dilution of the sea at the close of the Tertiary (Nikolsky 1978) or the lack of productivity in streams diluted with cold glacial water (Northcote 1967). Although it is not clear how spawning migrations developed in the Colorado squawfish this behavior probably developed in response to the adverse conditions of the Colorado River System. 34