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We evaluated the accuracy and precision of age estimates from ground sagittal otoliths, sectioned pectoral fin rays, and whole branchiostegal rays of Longnose Gar Lepisosteus osseus and Spotted Gar Lepisosteus oculatus using fish marked with oxytetracycline (OTC). The presence of OTC time stamps in these calcified structures and the ability to correctly identify post–time stamp annuli varied greatly. We identified time stamps in 66.7% and 91.7% of the otoliths and 43.8% and 61.4% of the pectoral fin rays for Longnose Gars and Spotted Gars, respectively; OTC marks were not observed in branchiostegal rays. Annual increment periodicity was validated in ground sagittal otoliths through age 10 for both species. For fish older than age 10, accuracy declined to about 60%, with most estimates being less than the number of post–time stamp annuli by 1 year. Age estimates derived from pectoral fin rays were consistently less than the number of post–time stamp annuli because OTC marks were generally associated with the outer edge of this bone. Overall accuracy from pectoral fin rays was only 14.3% for Longnose Gars and 22.6% for Spotted Gars. Although the lack of time stamps in branchiostegal rays prevented formal evaluation, age estimates derived from this structure were substantially lower than those from otoliths. Precision among readers was poor for all structures, reflecting the difficulties associated with age estimation for these two species. Based on our evaluation, past age estimates from branchiostegal rays and pectoral fin rays should be considered suspect. Ages derived from sagittal otoliths can be reliable through age 10. However, we recommend that readers verify their ability to produce accurate estimates and consider the implications of underestimating age for fish greater than age 10. Future efforts should work to refine or develop alternative preparation procedures for otoliths to improve the visibility of annuli and validate age estimates for older age‐classes.

In diet studies, stomach contents from predatory fish may be difficult to identify due to digestion. The Gizzard Shad Dorosoma cepedianum is an important prey species for sport fish; thus, determining the size of ingested shad can assist with evaluating competitive interactions, bioenergetic patterns, and niche partitioning and can add precision to predictive models. The gizzard organ of clupeids appears to be more resistant to digestion compared to other tissues and can often be found in the stomachs of predatory fish after other tissues from Gizzard Shad are digested. If the gizzard diameter is proportional to Gizzard Shad weight or length, it could be a useful structure for estimating the size of partially digested Gizzard Shad when other structures that are traditionally used to estimate weight or length (e.g., backbones) are damaged due to advanced digestion. For this reason, we evaluated the allometry relating gizzard diameter and Gizzard Shad weight and TL. We sampled a total of 936 Gizzard Shad from nine Oklahoma reservoirs. Fish were frozen and later thawed; they were measured for weight (±0.01 g) and TL (±1 mm), and the gizzard was then removed. Gizzard diameter was measured (±0.1 mm) at its widest point using calipers. Eight different equations were evaluated to find the best relationship (lowest Akaike’s information criterion) between gizzard diameter and weight or length. The relationship between gizzard diameter and fish weight was best modeled as a second‐order polynomial, whereas the relationship between gizzard diameter and fish TL was best described by a five‐parameter Richard’s equation. Both relationships explained over 80% of the variation in Gizzard Shad size. The 95% CIs for weight (±4–7%) and TL (±2–7%) indicated good overall precision for mean fish size based on gizzard diameter. Therefore, we recommend using gizzard diameter to determine weight and TL from diet samples when advanced digestion of Gizzard Shad limits the use of more traditional metrics (TL, backbone length, etc.).