The potential utility of pelvic fin rays as ageing structures was evaluated for southern US muskellunge Esox masquinongy mm. This evaluation indicated that pelvic fin rays may prove to be a useful, non‐lethal method for ageing muskellunge in southern US waters. Validation studies are still needed to ensure that growth rings form consistently throughout fish’s life span. 14 ± 2 SE) estimated absolute error between observed and predicted length changes for 13 tagged muskellunge was 30 Mitchill populations by comparing age estimates among three readers and against cleithrum estimates, and by comparing observed length changes of tagged fish with changes predicted from growth equations based on pelvic fin ray age estimates. Mean coefficient of variation in age estimates among all readers and between the two readers with prior ageing experience was 17.8% and 5.6%, respectively. Exact and within 1‐year agreement rates between pelvic fin rays and cleithra were 76% and 100%, respectively. Mean (±