Health evaluation of the sexually mature Crassostrea belcheri (G.B. Sowerby II, 1871) in an enclosed rearing condition

Abstract

Studies on the health status of a variety of oyster species in aquaculture have been widely reported, except that of Crassostrea belcheri despite its commercial significance. The quality of the oyster depends greatly only on the physiological conditions of the broodstock. The present study aimed to evaluate ultrastructures, presence of apoptotic cells, and other histopathology of sexually mature C. belcheri to provide basic information of this commercial oyster species. The oyster specimens of each sex were randomly sampled (n = 5) and cultivated under the aquaculture laboratory and the water quality within acceptable limits for broodstock oyster culture. The specimens were processed using the histology, ultrastructure, and terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) assay. We demonstrated that the selected organs including gill, mantle, and gonads showed no abnormal histopathological findings, as commonly found in the oyster histology. No apoptosis was observed in general. The ultrastructure of gametes appeared normally chartered. However, with high magnifications, brown cells were observed in the lamina propria of the stomach, indicating that the sampled oysters were under certain physiological stress. Our findings and reports on the ultrastructure and histopathology of C. belcheri could provide baseline information on health conditions for aquaculture design and maintenance to pursue higher reproductive success of the oyster in aquaculture settings.