Validating daily otolith increment formation in young of the year pagellus acarne in the Çanakkale region

Accurate age estimation is essential for population dynamics modeling and fisheries management. Otoliths serve as a critical resource for age determination in ichthyological studies, capitalizing on the embedded growth increments. The periodicity of these increments, however, requires thorough validation to confirm the accuracy of age assessments. This study validated daily increment deposition in sagittal otoliths of young-of-year Pagellus acarne from & Ccedil;anakkale, Turkey using Alizarin Red S (ARS), a fluorescent calcium-binding marker. Specimens (n=107; 1.8-4.7cm TL) were exposed to ARS concentrations of 0 (control), 50, 100, 150, 200, and 300mg/L for 24h, then reared 13 days. After a recovery period of 13 days, the second dyeing was performed with the aim of having a specific fluorescent mark to test the 13 rings found between the 2 fluorescent marks. Otoliths were examined under fluorescent microscopy. ARS marks were detectable in 81.57% of otoliths at >= 100mg/L, with the highest visibility at 300mg/L. Survival exceeded 84.2% across treatments. Increment counts between the first and second ARS marks (13 days) and from the second mark to the edge (20 days) matched elapsed time. Ages from wild fish (n=95) ranged 39-201 days with a growth rate of 0.176mm/day. This research demonstrates ARS is an effective, low-impact tool for periodicity validation and provides the basis for accurate age determination and population modeling of this ecologically important species in the region.