Comparison of Transverse and Sagittal Otolith Sectioning for Aging Wild Rainbow Trout from East Tennessee Streams

Rainbow trout (Oncorhynchus mykiss) are important sport fish that contribute to the economy and tourism in East Tennessee. Reliable aging techniques are needed to obtain accurate knowledge of their growth and productivity, which is necessary for making proper management decisions. Scales have historically been used for aging rainbow trout, but recent studies indicate that ages obtained from otoliths are more accurate. Preparing transverse otolith sections for aging is costly and time-consuming. Sagittal otolith sectioning is a more efficient alternative to transverse sectioning. Sagittal otolith sectioning has been examined for aging wild rainbow trout from the Southern Appalachians, but the need for better data on older fish (≥ age 5) exists. To address this need, two readers independently aged transverse and sagittal otolith sections from 682 wild rainbow trout from 10 East Tennessee streams. Aging accuracies for otoliths ground to the sagittal midplane were 99%, 84%, and 94%, respectively for ages 0-2, but declined from 85% to 20% for ages 3-6. Despite this decline, ages from sagittal otolith sections underestimated true fish ages (obtained from transverse otolith sections and previously validated with known-age fish) by only one year. Although ages obtained from otoliths ground to the sagittal midplane were less reliable than transverse-section ages for older fish in this study, they are still more reliable than scale ages.