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~ ; SPECIES BACKGROUND Habitat requirements, spawning locations, movements of young and adults, • tolerances to environmental parameters, and other fundamental information about Colorado_squawfish were- more fully documented in the 1980'x, when new, better technology and sufficient funds enabled accellerated research. During the last decade workers have located spawning and nursery areas and documented movement and migration patterns of young and adult fish (Haynes et al 1984, Thus 1985,1986, Tyus and- McAda 1984, Tyus et al 1982a,1987, Wick et al 1983.) Areas of relative density for adults, juveniles, and young have been mapped, and management strategies drafted (Archer et aI 1986, USFWS 1987). A1soJ the behavior and response of the fish to the environment were documented in hatchery (Hamman 1981,1986; Toney 1974), and laboratory (Berry, 1988, Berry and Pimental 1985, Black and Bulkley 1985ab, Rarp and Tyus (1989), Marsh 1985, Pimental et al 1985, Paulin et al. (1989)). The Colorado squawfish has a complex life cycle. Evolving in the depauparate fauna of the historic Colorado River Basin, this large predaceous fish is a generalist species, adapted to the large seasonal water fluctuations, low food base, and changing riverine subsystems of the Colorado River (M.Smith 1981, G. Smith 1981, Tyus 1986). Cyprinid species presumably invaded the new world from Asia in the Miocene epoch, and fossil Colorado Riverine Ptychocheilus species have. been reported from Pliocene (Miller 1961). We must assume that Ptychocheilus survived by incorporating life strategies to deal with changing climates varying from and to pluvial, incorporating 4