Oysters in the outback: oyster spat culture in potassium deficient inland saline GROUNDwater.

The increasing prevalence of oyster diseases has had both direct and indirect impacts on oyster production world-wide. Beyond initial stock losses during disease outbreaks, secondary imposts can arise from biosecurity protocols enacted to protect unaffected populations. By moving hatcheries to locations where the disease is absent, where carriers are not present and where introduction of the disease is less likely, risks can be reduced. One such option in New South Wales, Australia, is to move inland where large supplies of saline water are available.

Considerable research effort has been invested into inland saline aquaculture in Australia, but to date the emphasis has been on the production of fish and crustaceans.  One challenge has been natural deficiencies in potassium in the saline ground water. For fish this has been addressed through potassium supplementation, but it is not known if this would be necessary for molluscs. This trial was undertaken as a preliminary assessment of the use of saline ground water for hatchery production of oyster seed before more extensive investigation is undertaken.  

Sydney rock oyster (Saccostrea glomerata) spat were taken to the Inland Saline Aquaculture Research Centre at Wakool in western New South Wales, where they were held at one of two salinities (17ppt and 33ppt) and one of 5 potassium concentrations (0, 25, 50, 75, and 100% of the concentration present in seawater at that salinity). Two additional treatments of 17ppt and 33ppt artificial seawater (Instant Ocean) were included as controls. Spat were fed a standard hatchery algal diet and growth (increase in shell height) and mortality were determined every 7 days for 3 weeks.

Spat survival was significantly reduced in potassium deficient saline ground water, with poorest survival in 0% potassium at 33 ppt. Growth was significantly reduced at 17 ppt in comparison to 33 ppt. Growth also differed significantly between potassium treatments with no growth in 0 and 25% potassium at both salinities. There was no significant interaction between salinity and potassium. Spat held at 50% potassium and greater showed significant increase in shell height, the equivalent of that observed in artificial seawater controls.  

Investigations into effects of potassium deficient saline groundwater on the physiology of Sydney rock oysters are ongoing.