Introduction

The culture of marine pearl oysters by ocean ranching is not only cumbersome due to legalities but also subject to high a degree of theft, environmental risks and loss. A method is developed to enable the development and management of an on-land extensible/adaptable tank system which is fed by seawater and driven by Solar energy, to keep costs at a minimum and to render the system sustainable. This concept is applicable to Pinctada spp.

The configuration of the tanks and piping system will be totally flexible to allow for manipulation of depth, water flow and holding conditions as required. Tanks may be added or reduced to accommodate the stock requirements.

This concept is designed and operated in the region of North Western and Eastern Sri Lanka.

Method

Culture tanks (8000 L each) are set up to a) on-grow pearl oyster spat, b) hold juvenile pearl oysters, c) on-growing adult pearl oysters, and d) hold and on-grow nucleated pearl oysters. The culture tanks may be held indoors, with suitable artificial lightening regimes; or as an out-door system, subject to ambient environmental conditions, with provision of shading as required.

The culture tanks will be matured and rendered non-toxic prior to placing live oysters in them. The tanks may be extended by addition of more tanks and also capable of being adapted into a modified re-circulating system with 10 percent sea-water exchange per day. The culture tanks may or may not contain a suitable substrate as required by the specific species cultured.

Juvenile oysters will be collected by divers and held in a separate tank to reach maturation until about two (2) years of age. The oysters will be held in woven mesh baskets and suspended at different levels within the tank. Oxygenation of tanks will be maintained, and salinity and temperature, water flow, dissolved oxygen levels monitored twice a day. In another tank, adult oysters will be maintained under natural lighting conditions, and naturally fed by the flow through system. Algal feed may be added to supplement the feeding while slowing down water flow, while aeration is maintained.

For nucleation, adult oysters will be maintained under suitable conditions until the operation is performed. For this, a range of natural materials (e.g. -coconut shell, grains of gravel) and artificial material will be used.

Prior to nucleation, the oysters will be fed and then held without food under water flow for four hours, and then anaesthetized with clove oil or Aquis S.

Gonadal nucleation will be performed by a trained technician, and nucleated oysters will be allowed to recover in a recovery tank maintained with sea water and aeration supply.

Once recovered, the nucleated oysters will be transferred into a growth tank and maintained for another 1.5 years with higher feeding rates. Each oyster will be X-rayed with a hand -held X-ray machine to determine the pearl growth rates

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SUBSTITUTE SHEETS (RULE 26)