Specimens of the Sydney rock oyster Saccostrea commercialis were deployed for a 3-month period at control and sewage disturbed marine locations in the Hunter Region, New South Wales, Australia. The DNA damage product,8-hydroxyguanine, was measured by GC/MS-SIM from chromatin extracts of the gill tissues of oysters to assess oxidative damage. The levels ranged from 11.5 to 18.8 modified bases per 10(7) guanine bases. Although the condition indices were significantly different between the Redhead control site (178.3+/-3. 6) and the Burwood sewage disturbed location (140.4+/-4.4), no significant differences in 8-hydroxyguanine concentrations were detected between the sites, and the concentration of 8-hydroxyguanine was not correlated to condition index. However, levels of the DNA base modification were correlated with the concentrations of bioaccumulated lead (r=0.84, P=0.036). This association provides in vivo evidence that the bioaccumulation of lead results in oxidative damage to DNA. An additional control and sewage disturbed site were included to investigate the relationship between heavy metal bioaccumulation and the condition index of deployed oysters. After the 3-month deployment period, the condition index was negatively correlated to concentrations of bioaccumulated mercury (r=-0.80, P<0.001), cobalt (r=-0.65, P<0.01), and nickel (r=-0.69, P<0.01), suggesting a strong negative influence of these metals at relatively low concentrations on the physiological condition of the oysters.
Adult Sydney rock oysters (Saccostrea commercialis) and Pacific oysters (Crassostrea gigas) were kept on commercial oyster leases at three intertidal sites in Port Stephens, New South Wales, and subtidally under an experimental raft at a fourth site between July 1988 and September 1989. Oysters were sampled from each site at approximately monthly intervals for chemical and histological analysis. Condition index and percentage glycogen of Pacific oysters were higher than those of Sydney rock oysters during winter and spring but tended to be lower during summer and autumn. Gonads of Pacific oysters matured two months earlier than those of Sydney rock oysters, with spawning being observed at all sites in October. Sydney rock oysters spawned later during December-January and did not lose as much condition after spawning as Pacific oysters.
The absolute amount of glycogen in the meats of both species dropped at the expense of protein and lipid as the oysters became fully ripe. For both species, general condition of the oysters was best when they were grown subtidally under the raft, although both species were badly affected by invasion of the protistan parasite Mikrocytos roughleyi at this site. Poorest overall condition for both species occurred at a site (Karuah River) that experienced decreased salinities and increased turbidity after rain. Highest condition indices were found in Sydney rock oysters, at the site most dominated by coastal conditions (Corrie Island).
The salinity tolerance range of the scallop Pecten fumatus Reeve was 25-40 g 1-1, of the pipi (clam) Plebidonax deltoides (Lamarck) and the flat oyster Ostrea angasi Sowerby, 20-45 g I-1, and of the blue mussel Mytilus edulis planulatus Lamarck and the Sydney cockle Anadara trapezia (Deshayes), 15-45 g I-1. All of these bivalves absorbed substantial amounts of the amino acid L-methionine directly from seawater.
Although oyster larvae and spat have been reared successfully on algal diets for many decades, these are expensive to produce and do not always synchronize with hatchery requirements; considerable research has been conducted to determine which and why certain algal species are most appropriate and to investigate substitutes to algal feeds. Algal concentrates, commonly used in the United States, have overcome some problems associated with fresh algal feeds. However, work continues to develop cheaper non-algal alternatives. Recent promising advances have been in the formulation and preparation of experimental microencapsulated diets. However, further work upon capsules is required before the process can be commercialized. The possibility of rearing and substituting marine yeasts and bacteria for algae is an exciting and cost competitive alternative even to the microencapsulation approach.
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