Abstract
Histological changes in the gonad of cultured blacklip pearl oysters (Pinctada margaritifera) were studied during the main reproductive season. Collection of oysters from culture stock held at Magnetic Island and Orpheus Island, north Queensland, was conducted between August 2003 and February 2004 and oysters from each site were collected every month. Samples of gonad tissue from the oysters were processed for histological analysis. The sex ratio of oysters at both sites was skewed towards males. Active gonad development was recorded in all months during the study. Results of this study indicate that reproduction of P. margaritifera at Orpheus Island and Magnetic Island is a continuous process between August and February, as shown by the presence of ripe and partially spawned oysters during the majority of this period.