Abstract
Abstract.- The gametogenic cycle of the black clam Chione fluctifraga of northwestern Mexico, collected from March 2009through February 2010, was studied using conventional histological techniques and oocyte modal analysis. A conditionindex was also determined. Clams exhibited a semi-annual gametogenic cycle. The species generated the first oocytecohort 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 mainspawning occurred during the warmest period (>28°C). Gametogenic activity seemed to be strongly regulated by watertemperature. The average growth rate of oocyte cohorts was calculated (0.41 ± 0.10 μm day –1 ), with the most rapid growth(0.67 μm day –1 ) from September through October. The condition index was higher in summer, but other peaks occurred inwinter, producing accumulation of nutrients from increased phytoplankton biomass. The female:male ratio was 1:1.3; nohermaphrodites were detected. A reproductive classification is proposed. These results can help regulate exploitationand establish off-limit periods for this clam in the Gulf of California.
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