Growth and spawning period of Sepia officinalis, (Lineaus, ۱۷۵۸) in the Algiers region (centre of Algeria)

A total of ۱,۳۶۴ specimens of Sepia officinalis (Lineaus, ۱۷۵۸), including ۶۴۳ females and ۵۳۲ males were measured from February ۲۰۱۰ to January ۲۰۱۱ 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 ۱۱.۶۸±۰.۰۳ cm and for males ۱۲.۰۴±۰.۰۴ 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 (۲۶.۹۳ cm for both sexes combined) and the growth coefficient K, of ۰.۳۸ yr-۱, was established using the ELEFAN method. A seasonal analysis of this coefficient shows a slowdown in growth in autumn and winter. The value of t۰ determined by the Pauly method is ۰.۷۰۴ y-۱. Relative growth shows a negative allometry of ۲.۵۵ for both sexes and a constant of proportionality is about ۰.۳۹۱. The study of the overall sex ratio showed a slight predominance of females with a ratio of ۱:۱.۲. In autumn and winter, the females predominate with ۶۷.۳% and ۵۲.۵%, respectively. Considering the gonad and the nidamento-somatic index, S. officinalis in the Algiers region seems to breed between March and July.

Keywords:

Sepia officinalis , Sex-ratio , Gonadosomatic index , Length-weight relationship , Algiers.