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We used a combination of techniques to determine mean length at various ages. Our goal was to utilize measured changes in length of individual fish as much as possible and minimize reliance on scale analysis. However, recaptures of juvenile and subadult Colorado squawfish were few so measurements of fish aged by various means, including scales (ages 2-7), were used for young fish. Aces 0-70-7 Colorado squawfish average 7.7 mm long at hatching (Snyder 1981). For age 1 Colorado squawfish, mean length was determined using measurements of all fish seined on June 28, 1989 from backwaters near RK 87. A unimodal size distribution indicated these were all of one age group. For Colorado squawfish 2-7 years old, mean length at each age was derived from measurements of fish aged using scale analysis. These fish were captured between April 28 and June 21 (1991-1994) primarily from the lower reach and many were therefore 2-3 months younger than the reported age. Thus, beginning with 2-year-old fish, annual increases in length represent growth from one spring period to the next rather than from one hatching period to the next. Scales were mounted wet on a microscope slide, a second slide was taped over it, and the scale allowed to dry inside. Scale images were magnified and projected for analysis using a Bausch and Lomb scale reader (Bausch and Lomb, Inc., Overland Park, Kansas). Scale annuli were counted and the missing first annulus (e.g., Seethaler 1978, Hawkins 1992) added to estimate age. Four to eight scales were examined from each fish and the number of annuli most frequently identified was used. We used scales from known-age, pond-reared Colorado squawfish (2-4 years old) for developing our technique and later testing our accuracy. Ages 8 and older For fish eight years old and older, sufficient recapture data were available for determining mean annual growth increments. Growth data were typically used from fish with capture- recapture intervals of 1 year. Thus, a growth increment for an individual fish was the difference in length at capture year i and year i + 1. However, because of low sample size for fish z 600 mm TL, annual growth increments were also calculated for fish with recapture intervals of 2 or 3 years (total gain in length divided by the number of years between captures). Growth increments were averaged by size class of fish at initial capture year i. Size classes were in increments of 50 mm (e.g., 300-349, 350-399, etc.). Analysis of variance (ANOVA) was used to test for differences in growth rates among size classes. Mean length at each age was first calculated by adding the appropriate mean increment of growth (based on length class) to the mean length of the preceding age. The average length of 7-year-old fish as determined from scale analysis was used as the starting point for these calculations. This process was continued until mean length reached 900 mm, roughly the upper size limit of Colorado squawfish captured from the Colorado River in recent years. A-5