Gametogenic cycle and variations in oocyte size of Tapes philippinarum from the Lagoon of Venice

The gametogenic cycle of the clam Tapes philippinarum was studied in two populations from different areas of the Lagoon of Venice: S. Angelo (central basin) and Chioggia (southern basin). Samples were collected at regular intervals from July 2000 to July 2001. The study was performed by microscopic observations of histological sections of gonadic tissue and by measuring follicular and oocyte sizes by image analysis. Gametogenesis began in January and was clearly evident until May. Ripe clams appeared in April, and most active spawning occurred in May, continuing during summer until September. Measurements performed using image analysis (i.e., follicular area, percentage of reproductive tissue, oocyte diameter, percentage of resorbing area) highlighted environmental differences between the two sampling sites, demonstrating the better condition of clams from Chioggia.