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INTRODUCTION Growth and survival rates are fundamental components of most demographic studies of long- lived species and are essential to understanding population dynamics. Determination of population status and trend and identification of factors limiting population increase are requisite to formulating recovery goals and management strategies for endangered species. Colorado squawfish (Ptychocheilus lucius), an endangered, long-lived, cyprinid endemic to the Colorado River system, has been the focus of much life-history research in recent years. Previous studies of age and growth of Colorado squawfish have relied on scale analysis, whereby age is determined by counting numbers of scale annuli and growth is estimated as the difference in calculated fish lengths predicted from relationships between length and radius of scale annuli (e.g., Vanicek and Kramer 1969, Seethaler 1978, Musker 1981, and Hawkins 1992). Problems inherent in scale-based aging and growth estimation for long-lived species prompted us to refine existing growth estimates of Colorado squawfish by utilizing newly available, mark-recapture-based, growth data. Age estimates derived from the refined growth estimates enabled us to also assess adult survival rates. Techniques used in scale analyses are fairly standardized (e.g., Tesch 1968, Carlander 1969). While results of such analyses have proven reliable for some species, for others they have been largely unreliable (Beamish and McFarlane 1987). Scales were considered by Scoppetone (1988) to be unreliable for accurately aging many western North American catostomids and cyprinids because age was considerably underestimated in long-lived individuals. Although validation of aging techniques using known-age fish is a critical component of studies attempting to estimate age and growth from scales, such validation is often lacking in non- game fish due to the scarcity of known-age individuals. Aging other bony structures (e.g., vertebrae, otiliths, opercles, etc.) may corroborate results from scales but this constitutes only a partial validation at best (Beamish and McFarlane 1983), and requires sacrifice of the animal. Problems specific to aging Colorado squawfish include the lack of annulus formation during the first year, and the compression and loss of outer annuli by older fish (Hawkins 1992). Lack of first-year annulus formation has been corrected by adding a year to the number of annuli (Seethaler 1978, Hawkins 1992), but problems with distinguishing and counting outer annuli can result in underestimation of ages and population age frequencies, resulting in many fish assigned to the age where the method fails (Beamish and McFarlane 1983, Hawkins 1992). Hawkins (1992) suggested that differences in average annual growth increments for Colorado squawfish > 500 mm TL, calculated from scales (30 mm/year) and those from recaptures of tagged fish (10-15 mm/year), may be due to a negative effect from Carlin dangler tags on tagged fish. Indeed, Floy tags, another type of external tag, reduce growth in trout (Carlin and Brynildson 1972, Mourning et al. 1994), though not in largemouth bass (Tranquilli and Childers 1982). The recently developed, small and internally-implanted Passive Integrated Transponder (PIT) tag enhances the ability to permanently mark individual fish and track growth through successive years. Burdick and Hamman (1993) reported 98-100 % tag verification 20-24