Abstract
Background:
The common octopus, Octopus vulgaris, is an ecologically and economically vital cephalopod species in the Mediterranean, yet its biological characteristics remain unstudied in Libyan waters.

Aim:
This study provides the first comprehensive analysis of growth patterns for this species along the western Libyan coast.

Methods:
A total of 390 specimens (172 males, 218 females) were collected monthly from January 2021 to January 2022.

Results:
Dorsal mantle length (DML) ranged from 5 to 25 cm and body weight (BW) from 63 to 3376 g, with no significant difference between sexes. A strong seasonal pattern was observed, with minimum average sizes recorded in August (~11 cm, ~340 g) and maximum sizes in January (~18 cm, ~1450 g). The length-weight relationship revealed negative allometric growth (b = 2.85) for both sexes, with a strong correlation (R² > 0.94) and no significant sexual dimorphism. The von Bertalanffy growth function estimated asymptotic lengths (L∞) of 30 cm for males and 28 cm for females, consistent with other Mediterranean populations but lower than Atlantic ones, suggesting biogeographical constraints. The condition index showed significant seasonal variation, with lows in March and peaks in June, likely linked to reproductive cycles.

Conclusion:
These results characterize a population with typical Mediterranean growth dynamics. The key finding of a pronounced seasonal recruitment pulse in late summer highlights the vulnerability of juveniles to fishing pressure. We recommend that fisheries management strategies, such as seasonal closures during this critical period, be implemented to ensure the sustainability of this valuable Libyan resource.

Key words: Octopus vulgaris; Length–weight relationship; Fisheries management; Libya; Mediterranean Sea.