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1 1 t ii 1981-1987 (Table 5). Included in this total were I88 "ripe" adults. These fish were classified "ripe" if milt or eggs could be expressed from the vent with light hand pressure on the abdomen. Ripe males (N=178) were always found heavily covered with breeding tubercles and bearing a bronze coloration. A total of 23 additional fish were classified as suspected male because of the presence of these two characteristics. Robust tuberculation in male Colorado squawfish has also been noted by Hamman (1931) and Seethaler (1978). Only 10 ripe or spent female Colorado squawfish were positively identified by expression of eggs. However, 40 additional fish were classified as suspected female because of their large size, and absence of heavy tuberculation and bronze coloration. These data indicate a definite paucity of adult female Colorado squawfish in the Green River system, which ma}• be due to differential mortality (Tyus et al. 1987). High male:female sex ratio in Colorado squawfish has also been noted by Seethaler (1978) (following a re-evaluation of Vanicek's (1967) data) and for other squawfish species (Patten and Rodman 1969). Larvae and Postlarvae: Following spring runoff, larval Colorado squawfish emerge as sac-fry from cobble bars in the Yampa Canyon and-drift downstream (Haynes et al. 1984, Tyus et al. 1982b) to concentrate in shallow backwater habitats of the Green River in Utah (Figure IO) (Tyus et al. 1982b, 1987). Young fish are able to use river transport for dispersal from upstream spawning grounds to these productive downstream nursery habitats (Tyus and McAda 1984, Tyus 19$6), habitats created by gradually decreasing summer flows. During this period of emergence and dispersal, yolk is fully absorbed and young fish reach a critical stage when feeding must begin. Postlarval (Young- of-year) Colorado squawfish are rare in the Yampa River and no Age 0 fish 23