Experimental deepwater culture of the Sydney rock oyster ( Crassostrea commercialis=Saccostrea cucullata) : I. Growth of vertical clumps of oysters (‘ren’)

Abstract

Japanese style ren, consisting of scallop shells encrusted with small Sydney rock oysters and strung on vertical wires, were grown at 23 estuarine stations along the New South Wales coast for up to 21 months. Weight increments of ren were used to evaluate growth rates of oysters in non-cumulative (3–4 months immersion) and cumulative (6–21 months immersion) series. Oyster weight increased at a rate of approximately 10% per month, which was considered suitable for commercial production, but estimated labour costs to make up the ren were high. Mortality rate was 6.3% per 3–4 months immersion. Gaping oysters, through natural mortality, winter mortality, the haplosporidian parasite Marteilia sydneyi, and other causes, accounted for 4.5%. Broken oysters, resulting from fish and crab predation, accounted for 1.8%. Mortality caused by the polychaete mudworm Polydora websteri was negligible; only 1.7% of the 4.5% gapers showed the characteristic blisters.