S. Steele, M.F. Mulcahy
Abstract:
A study was conducted from April 1996 to December 1997 on Crassostrea gigas grown in two sites on the south coast of Ireland. This is the first study on the reproductive biology of C. gigas in Ireland. Gametogenesis was examined by histology, and related to temperature, food availability (Chlorophyll a) and condition indices as well as parasite burden and pathology. In site 1 (Dungarvan) oyster spawned in the summer of both years of the study. Oysters were infested with the parasitic copepod Mytilicola orientalis and the polychaete Polydora sp. In site 2 (Cork Harbour), oysters did not spawn in either year of the study and gonadal resorbtion occurred. Oysters were infested with Polydora sp. and also showed shell blistering indicative of the influence of the pollutant tributyl tin. There were no significant differences in chlorophyll a or temperature between the two sites, leading to the conclusion that failure to spawn may have been pollution related. The impact of spawning and resorption of gonad in the oysters on protein, glycogen and lipid levels of selected tissues was assessed. When the oysters in site 2 did not spawn, they started a process of gametic degeneration and resorption. This process has not previously been fully described in Crassostrea gigas. The process of resorption of gametes was described and in females, was examined ultrastructurally.
(Department of Zoology and Animal Ecology, National Unversity of Ireland, Cork, Ireland)