Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Gametogenic cycle and monthly variations of oocyte size in the invasive cockle Fulvia fragilis (Bivalvia: Cardiidae) from the Bay of Tunis (northern Tunisia, central Mediterranean).

Abstract

This is the first study on the gametogenic cycle of the cockle Fulvia fragilis, lessepsian successfully established species throughout the Tunisian coast and especially, in northern areas, such as the Bay of Tunis. 6437 oocytes were measured from 73 specimens of F. fragilis collected from April 2006 to April 2007. The recorded data allowed us to show that F. fragilis had a continuous gonadal activity with significant gametogenic regeneration. Significant differences were found between the mean oocyte diameter for the various stages of sexual maturity (ANOVA, P<0.05). Throughout the study period, all categories of oocytes (previtellogenic oocyte, vitellogenic oocyte and mature oocyte) were observed during all gametogenesis stages, except during the early stages. This continuous gametogenic production was related to the successive spawns observed. These latter could explain the successful establishment of F. fragilis in its new areas and as a consequence, of its fast geographical expansion, not only in the Tunisian waters, but also, throughout the Mediterranean Sea.