Comparison of Aging Methods and Validation of Otolith Ages for the Rainbow Darter, Etheostoma caeruleum
Etheostoma caeruleum were sampled from the James River, southwest Missouri, during eight months, July 1996 through May 1997. Ages were estimated from whole and sectioned otoliths (sagittae) and from scales by counting annuli. Edge analysis indicated that otolith annuli (opaque zones), visible in whole and cross-sectioned otoliths, formed yearly, primarily during July through September. In contrast, scale edge analysis indicated no clear pattern of annulus formation. Independent readers agreed on 63–73% of ages using otoliths but only 38% of ages using scales. Sectioned and whole otolith age estimates made by one experienced reader agreed for 68% of individuals. Scales underestimated age compared to otoliths, and maximum otolith age was five years.Abstract
Relationship of observed frequency of occurence of three margin conditions in scales of Etheostoma caeruleum versus month of capture, 1996–1997. Margin condition was based on the estimated degree of completion of the annulus at the growing edge of the scale: (+) annulus forming at the margin, (++) substantial scale growth beyond the last annulus, (+++) scale apparently near the formation of the next annulus. Numbers above the x-axis indicate sample sizes
Relationship of observed frequency of occurrence of opaque zones (annuli) at the growing margin in whole and sectioned otoliths (sagittae) of Etheostoma caeruleum by month of capture, 1996–1997. Numbers next to the points indicate sample sizes. Differences in sample sizes are caused by samples lost or damaged during sectioning
Frequency distribution of age estimates for Etheostoma caeruleum using three aging methods