Age estimation of native desert catostomids is essential for understanding sucker population dynamics, but is poorly studied. Flow of the Lower Salt River in central Arizona is controlled by a hydroelectric dam, with fish growth subject to the modified flow regime and temperatures of the reservoir’s hypolimnion. These flows differ from natural flow patterns and temperatures characteristic of Southwestern rivers, which may affect the growth and ageing patterns of the fish present. There is little research on the ageing of Sonora Suckers Catostomus insignis, with less information on the ageing of these fish subjected to an abnormal hydrologic regime. This research demonstrates the effects of irregular flow regimes on ageing and the growth of native catostomids. To quantify the environmental-driven variation in ageing, weight, length, and age estimates from 58 Sonora Suckers from two Arizona river systems were compared, one’s flow controlled by a hydroelectric dam (Salt River) and another undammed (Blue River). Pectoral fin rays and otoliths were removed in dissection, epoxied in a West System 105 resin and hardener, and sectioned using a slow-speed Isomet saw. Structures were imaged under a Leica MZ16 Stereo Microscope, and aged by a single reader. Comparing age estimates for otoliths and pectoral fin rays, structure age agreement was assessed to be 23%. The maximum age for the Blue River was 12 years old at 372mm, with Salt River was 15 years old at 540mm. Age-at-length keys, length frequencies, minimum and maximum ages, growth rates, and visible comparison of the annuli production between both populations demonstrate the variability caused by abnormal flow peak timing. Field data collection and analysis is underway. Results will be reported in a thesis and a publication.