Methodology for processing and interpreting annual increments in Gray Redhorse otoliths with implications for other catostomids

Abstract Objective Age data are widely collected in fisheries science because of the vital information it provides about population characteristics. Moxostoma, a common genus of Catostomidae, are abundant throughout North America, yet there are few studies that focus on methodological procedures to estimate age for these species. Moreover, studies that have concentrated on estimating age of Gray Redhorse M. congestum, a species whose otoliths look very similar to those of other catostomids, are also uncommon. Therefore, we wanted to present insight into the morphological features, processing methodologies, and interpretation of annual increments in Gray Redhorse otoliths to provide guidance and consistency for aging this species and other catostomids. Methods Gray Redhorse were collected from central Texas rivers quarterly throughout 2021. The lapillus otoliths were removed, morphologically assessed, sectioned, and imaged for annual increment interpretation. Results and conclusion All of the whole otoliths presented uniform characteristics, including presence of a gibbus maculae (i.e., a hump). In the sectioned otoliths, the annual increments were easily distinguishable for ages 1–4. Otoliths aged ≥5 presented some difficulties due to shading or darkening of increments; therefore, we suggest finding and counting annual increments on the lateral edge of the structure. Furthermore, a completed annulus should be counted as an opaque zone that is characterized by either a thin brown or a distinct thin dark-gray line, paired with a translucent zone. Given that Gray Redhorse otoliths have a morphology and increment patterns that are similar to those of other catostomids, the methods and interpretation of increments in otoliths presented here can likely be applied more broadly to the family.