Effectiveness of Alizarin Red S Immersion for Validating Otolith Daily Growth Increments in Juvenile Sharpsnout Seabream (Diplodus puntazzo)

This study validates daily increment formation in otoliths of juvenile sharpsnout seabream (Diplodus puntazzo) from the Dardanelles using Alizarin Red S (ARS) marking at four concentrations (50, 100, 150, and 200 mg/L). Eighty wild-caught juveniles (20–76 mm total length) were subjected to 24-hour ARS immersion, followed by 10 days of captivity. Mortality varied among treatments, with cumulative rates of 5.9–12.5% across ARS groups and 6.7% in the control, with the highest mortality occurring in the 100 and 200 mg/L groups (12.5% each). ARS marks were successfully detected in 75.3% of examined otoliths, with mark quality increasing at higher concentrations. Chi-square analysis comparing increment counts between the ARS mark and otolith edge with elapsed time revealed no significant difference (χ² = 0.355, df = 55, P = 0.93), confirming daily periodicity of increment formation. Based on the balance between marking success and fish survival, 50–100 mg/L represents an optimal concentration range for future studies. These findings provide robust validation for daily age estimation in juvenile D. puntazzo from the Dardanelles, supporting age-based growth studies and fisheries management in this ecologically important region.