Gametogenic cycle and condition index of the clam Chione fluctifraga in Bahia San Jorge, Gulf of California, Mexico

The gametogenic cycle of the black clam Chione fluctifraga of northwestern Mexico, collected from March 2009 through February 2010, was studied using conventional histological techniques and oocyte modal analysis. A condition index was also determined. Clams exhibited a semi-annual gametogenic cycle. The species generated the first oocyte cohort in spring (April) started its vitellogenic growth and remained continuous over 9 months until early winter (December). A resting period occurs in winter. Clams released gametes continuously throughout the reproductive period, but the main spawning occurred during the warmest period (>28 degrees C). Gametogenic activity seemed to be strongly regulated by water temperature. The average growth rate of oocyte cohorts was calculated (0.41 +/- 0.10 mu m day(-1)), with the most rapid growth (0.67 mu m day(-1)) from September through October. The condition index was higher in summer, but other peaks occurred in winter, producing accumulation of nutrients from increased phytoplankton biomass. The female: male ratio was 1:1.3; no hermaphrodites were detected. A reproductive classification is proposed. These results can help regulate exploitation and establish off-limit periods for this clam in the Gulf of California.