Age and Growth of Roundtail Chub in the Upper Verde River, Arizona

Abstract

AbstractEstimates of the age and growth of roundtail chub Gila robusta were made by analyzing thin cross sections of sagittal otoliths from 280 specimens collected in the upper Verde River, Arizona, from January 1997 to December 1999. Marginal increment analysis indicated that a single annulus completed formation between January and May. The use of otoliths to age roundtail chub was further validated using otoliths of known‐age, hatchery‐reared fish for which (upon examination) the number of annuli agreed 100% of the time with the true age of the fish. In addition, daily increments were observed on sagittal otoliths of age‐0 roundtail chub and, when counted, agreed with the true age of fish 70% of the time; daily ring counts were within 1 and 2 d of the true age 80% and 90% of the time, respectively. Ages assigned to wild‐caught fish by three independent readers resulted in a coefficient of variation (100 × SD/ mean) of 8.2. Ages of roundtail chub varied from 1 to 7, the largest fish being a 427‐mm total length (TL), 836‐g total weight (TW), age‐7 female. The largest male was 413 mm TL, 629 g TW, and age 6. The growth of age‐1–7 roundtail chub (both sexes combined) was greatest during the first year and was best described by the equation Lt = 499.30 [1 − e−0.23(t−0.147)], where Lt is length at time t.