A standardized method for age estimation of little tunny (Euthynnus alletteratus) using dorsal fin spines

Age and growth of little tunny (Euthynnus alletteratus) were assessed by examination of annual growth increments in cross-section of first dorsal spines from 207 fish (85–1030 mm Straight Fork Length, SFL) sampled between 2017 and 2021 from the northeastern Atlantic and Mediterranean Sea. Some analysis and recommendations are provided for using the first dorsal fin spine for age estimation of little tunny. The comparative analysis of the sectioning location, with transverse sections collected at 0.5, 1.0, and 1.5 times the width of the condyle base measured from the base of the spine, showed that the 1.0 cross-section distance proved to be the most reliable option. Fish ages ranged 0–10 years old and the growth parameters estimates based on standard von Bertalanffy growth function were (for sexes combined): L_∞ (asymptotic length) = 99.77 cm; k (growth coefficient) = 0.445 year⁻¹; and t₀ (age at zero length) = − 0.072 year⁻¹. In order to ensure comparable results, it is crucial to implement a reproducible protocol for future studies on the age and growth of little tunny.