The ages of 229 white suckers Catostomus commersonii from six drainages in the upper Missouri River basin were estimated from scales, pectoral fin ray sections, and lapilli otolith sections to evaluate the potential bias of age estimates between structures. Age estimates were compared by calculating the coefficient of variation, average percent error, percent agreement, and percent agreement within 1 year, as well as by constructing age bias plots. Overall, the relative precision of age estimates from pectoral fin rays and otoliths was higher than that of age estimates from scales and otoliths, but neither pair differed in precision from scales and fin rays. The relative precision of age estimates between pairs of structures was variable both within and among drainages, and few trends could be detected. The percent agreement between structures ranged from 50.0% to 93.8% among drainages, but 9 of 18 pairs had agreement rates greater than 70.0%. Percent agreement within 1 year was greater than 85.0% for all pairs of structures in all drainages. Age estimates from scales underestimated the age estimates from pectoral fin rays and otoliths beyond age 3, while pectoral fin rays only slightly underestimated ages from otoliths of fish older than age 6. We recommend sectioned lapilli otoliths for estimating the age of white suckers, especially if mature individuals are present in the population and lethal collection techniques are allowed. Pectoral fin ray sections are the best nonlethal structure for estimating the age of white suckers but may underestimate the ages of fish older than 5 years. Scales remain suitable for estimating the ages of immature fish, but their use is not recommended for mature fish. This information will allow fisheries managers and researchers to select the most appropriate structure for use in future age assessment studies of white suckers and other catostomid species.

Seven Plains Minnows, Hybognathus placitus, Family Cyprinidae, were collected on 11 June 2003 from Morgan Creek, in Grasslands National Park, Saskatchewan, Canada. This collection is the first record of the species in Canada and extends the northern distribution limit of the species. Of 95 Hybognathus spp. collected at the site, only eight specimens were retained for positive identification because of the uncertain status of two conspecifics, the Western Silvery Minnow, H. argyritis, and the Brassy Minnow, H. hankinsoni, in Saskatchewan. Our findings should stimulate additional sampling to assess the identification and status of Hybognathus spp. in southwestern Saskatchewan. Accurate field identification of Hybognathus spp. remains an issue and collection of all specimens is recommended to accurately identify members within the genus.