Aspects of the reproductive biology of the velvet belly, <Etmopterus spinax> (Elasmobranchii : Squalidae)

Abstract

Aspects of the reproductive biology of the velvet belly, Etmopterus spinax are presented in this paper. The observed specimens were collected off Tunisian coasts and the coast of Languedoc (southern France), in sandy and/or muddy bottoms from 100 m to 400 m depth. The males were adult over 350 mm total length (TL). Females matured between 310 mm and 370 mm TL. The smallest adult female with ripe oocytes ready to be ovulated and the smallest gravid female were 380 mm and 400 mm TL respectively. All females over 400 mm TL were adults. The maximum size was 460 mm for both sexes. Gestation could be a minimum of one year, but it is hypothesised that it may be as much as two years. Vitellogenesis did not proceed in parallel with gestation. However, in a single pregnant female developing oocytes were observed. Vitellogenesis continued after parturition which occured generally in summer. Average TL and average weight of fully-developed fetuses were 126 mm and 6.03 g. A calculated chemical balance of development (CBD) based on mean dry-weights of fully-developed fetuses and ripe oocytes was 0.803. This low value is due to a degree of lecithotrophy in E. spinax; even if the mother role during gestation is not negligible. Fecundity ranged from five to nine newborn pups per brood. Ripe oocytes were more numerous in the left organs; generally embryos and fetuses were symmetrically distributed in each uterus, although in some specimens they were more numerous in the left uterus.