Growth and spawning period of Sepia officinalis, (Lineaus, 1758) in the Algiers region (centre of Algeria)

A total of 1,364 specimens of Sepia officinalis (Lineaus, 1758), including 643 females and 532 males were measured from February 2010 to January 2011 catching by the commercial trawling fisheries of Algiers region. The sex, dorsal mantle, wet body mass, nidamental gland weight and female gonadal weight were recorded. The mean length of the dorsal mantle for females was 11.68±0.03 cm and for males 12.04±0.04 cm. The difference between the two averages was not significant. The Powell-Wetherall method for determining the asymptotic dorsal length of the mantle (DML∞) was applied (26.93 cm for both sexes combined) and the growth coefficient K, of 0.38 yr-1, was established using the ELEFAN method. A seasonal analysis of this coefficient shows a slowdown in growth in autumn and winter. The value of t0 determined by the Pauly method is 0.704 y-1. Relative growth shows a negative allometry of 2.55 for both sexes and a constant of proportionality is about 0.391. The study of the overall sex ratio showed a slight predominance of females with a ratio of 1:1.2. In autumn and winter, the females predominate with 67.3% and 52.5%, respectively. Considering the gonad and the nidamento-somatic index, S. officinalis in the Algiers region seems to breed between March and July.