Age validation in the pharaoh cuttlefish (Sepia pharaonis Ehrenberg, 1831) using cuttlebone increments: Insights from reared individuals and comparison with wild populations

Nimija, P M and Laxmilatha, P and Mini, K G and Vidya, R and Linga Prabu, D and Kavitha, M (2026) Age validation in the pharaoh cuttlefish (Sepia pharaonis Ehrenberg, 1831) using cuttlebone increments: Insights from reared individuals and comparison with wild populations. Fisheries Research, 302. pp. 1-8. ISSN 0165-7836

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Abstract

Reliable age estimation is essential for understanding growth and population dynamics in cephalopods. This study analysed cuttlebone increment deposition in reared (n = 286) and wild (n = 385) Sepia pharaonis to evaluate increment periodicity and assess the applicability of cuttlebone-based ageing approaches. Embryonic examination showed that lamellar formation begins before hatching, with 6.6 ± 0.5 increments present prior to hatching, increasing to 7.2 ± 0.9 on the day of hatching. In reared juveniles, number of increments increased consistently with chronological age (R² ≈ 0.994), broadly supporting a near-daily increment accumulation pattern under controlled conditions, although interval-specific deposition rates varied during the first 100 days of growth. Wild individuals exhibited greater variability in the relationship between number of increments and mantle length across a broader size range (40–350 mm DML). Within the overlapping DML range of 40–75 mm, wild individuals generally possessed fewer increments than reared individuals, suggesting that environmental variability, differences in somatic growth, or a combination of both may influence increment deposition patterns under natural conditions. These findings support near-daily increment formation during early life stages in reared S. pharaonis and provide an improved foundation for age estimation, growth modelling, and stock assessment of this commercially important species.

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