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90 JOURNAL OF THE ARIZONA-NEVADA ACADEMY OF SCIENCE VOL. 21 Table 1. Variation in age estimates obtained from different bony structures of individual razorback sucker caught from .-: Lake Mohave, Arizona and Nevada. If one age (structure) was considered most reliable on the basis of clarity of presumed annular marks, it is so indicated by boldface and italics. Specimen Origin and Date Scales Branchio- stegal Rays Pectoral fin-rays Vertebral Centra Opercular Bone Cleithral Bone Otolith Section DNFH, 1982 25 28 24 23 28 27 - DNFH, 1982 24 35 34 21 41 16 - DNFH, 1982 25 17 27 19 30 24 28 DNFH, 1982 23 20 23 22 32 20 32 CADFG, 1983 21 17 25 13 23 21 - CADFG, 1983 17 20 25 16 25 15 - CADFG, 1983 26 24 25 20 38 22 - CADFG, 1983 17 17 27 17 24 25 25 CADFG, 1983 12 13 21 12 20 10 25 CADFG, 1983 15 16 23 19 23 20 25 CADFG, 1983 26 23 18 26 24 21 25 CADFG, 1983 23 21 28 20 27 28 28 CADFG, 1983 24 16 25 12 31 12 33 CADFG, 1983 29 25 23 21 27 19 34 A B Figure 2. A. Scanning electron micrograph (18X) of scale from a razorback sucker caught from Lake Mohave, Arizona and Nevada, 32 years of age by otolith section; note absence of evident annuli and patterns of wear on surface and margin. B. Detail for lightened portion of A (180X), showing uniformity of circuli. Beamish and McFarlane 1983). All these bones may be usable if sectioned and polished (e.g., Scoppettone et al. 1986), which was not attempted. Our data for scales of wild-caught fish indicate that standard LM or SEM examination (the latter at magnifica- tions of more than 5000X) varies from questionable to perhaps useless for age estimation in razorback sucker (see also: McAda and Wydoski 1980, Minckley 1983). Scales were thickened, irregularly shaped, centrally scarred, eroded, or regenerated, or circuli were so uniform in distribution that annular marks were indiscernible by methods applied (Fig. 2). Examination of different scales from a single fish resulted in vastly differing age estimates. Those from one individual varied from 0 to more than 25 complete marks, and 3 of 7 scales from another fish showed no evident annuli, while the other 4 indicated ages of 12 to 23 years. Estimates for 14 Lake Mohave fish, excluding scales that showed no evidence of annuli and using minimum ages from selected scales with marks extending across the entire structure, varied from 12 to 29 years (Table 11. Fin rays presented similar problems, since each lobe of a single section varied in number of complete marks and rays from the same individual indicated different ages. External counts on unsectioned otoliths of wild-caught fish were also compromised, similar to those on skull bones and vertebrae, by dense ossification and irregular configu- ration. Large sagittae were thickened, rugose, and opaque (Fig. 3), with apparent growth most rapid along the anterior, posterior, and dorsolateral sides. Marginal growth appar-