Reproductive Biology and Maturity Characteristics of the Spineless Cuttlefish Sepiella inermis (Van Hasselt, 1835)

Rosmy, A V and Laxmilatha, P and Nimija, P M and Vidya, R (2026) Reproductive Biology and Maturity Characteristics of the Spineless Cuttlefish Sepiella inermis (Van Hasselt, 1835). Thalassas: An International Journal of Marine Sciences, 42. pp. 1-14. ISSN 0212-5919

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Abstract

The reproductive dynamics of Sepiella inermis were investigated from February 2022 to December 2024 to examine temporal patterns in sex ratio, maturation, fecundity, and reproductive indices. A total of 1,313 individuals were analyzed. The overall sex ratio was significantly female-biased (1:1.31, male: female; χ² = 23.9, p < 0.001), with significant female dominance during pre- and post-monsoon seasons, while no deviation from parity occurred during the monsoon. All maturity stages were recorded throughout the study period. Spawning females predominated in most months, whereas spent males were frequently observed, indicating prolonged reproductive activity with asynchronous maturation. The length at 50% maturity was estimated to be 49 mm dorsal mantle length in females and 39 mm in males. Absolute fecundity ranged from 85 to 602 eggs (mean = 271) and increased significantly with dorsal mantle length (R² = 0.73) and body weight (R² = 0.84). Relative fecundity (2–11 eggs g⁻¹) showed no consistent relationship with size. Gonadosomatic and nidamental gland indices showed significant monthly variation (P < 0.001), whereas the overall effect of year was not significant (P > 0.05); significant month × year interactions indicated interannual differences in the magnitude of monthly variation. Both indices showed higher values during October–March, indicating seasonal intensification of reproductive activity. These results indicate prolonged reproduction with seasonal intensification and provide biological information relevant to stock assessment and management.

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