Seasonal changes in the gonadal state of the oysters Crassostrea iridescens and Crassostrea corteziensis (Filibranchia: Ostreidae) in the Northwest coast of Mexico

Abstract

The reproductive cycle in oysters has been the object of several studies in temperate zones. However, little information is available for tropical and subtropical species. This study shows the seasonal changes in the gonadal index (GI) of two species of oysters, Crassostrea iridescens and Crassostrea corteziensis, which differ markedly in their habitat and time of reproduction. Both oysters were sampled at 45 days intervals in the Northwest coast of Mexico between November 1989 and October 1990. Gonadal and somatic tissue per individual were dried for three days at 90°C, weighed and recorded. The gonadal index (GI) applied in this work was calculated from: GI = Wg/Ws. Where Wg is the average gonadal tissue dry weight, and Ws is the average somatic tissue dry weight. Seasonal variations in the gonadal state were evident for the two species. C. iridescens exhibited only a single maximum in the year, while C. corteziensis two peaks. This situation is presumably related to the contrastable environmental conditions that prevail in the sites where each species inhabit.