GONADAL DEVELOPMENT AND HISTOCHEMISTRY OF THE TROPICAL OYSTER, CRASSOSTREA CORTEZIENSIS (HERTLEIN, 1951) DURING AN ANNUAL REPRODUCTIVE CYCLE

We describe the quantitative and qualitative histology and histochemistry for a tropical oyster, C. corteziensis sampled in a coastal lagoon in Northwest, Mexico. Males were larger than immature oysters, with females presenting intermediate values. In this species, mature organisms were found most of the year, and there were at least two strong spawning periods, one in summer and the second in autumn. The presence of mature oocytes most of the year did not allow for differentiation of an annual reproductive pattern using average oocyte diameter, as has been used in other species. There was a very short resting period in winter, particularly in December 2005 and by January to February 2006 postvitellogenic oocytes can already be found. Both sexes tended to have more lipids in the gonad tissue as maturation advanced, with an inverse correlation to carbohydrate in gonad and in vesicular tissue in females. No differences in lipids or carbohydrates content were found in digestive gland. A negative correlation was found between chlrophyll a content and gonad coverage area in males and females. Maturation occur at sea surface temperatures higher that 20 degrees C, and spawning when temperature increases above 27 degrees C.