Summary

Objectives

1. To induce tetraploidy in Sydney rock oyster larvae.
2. To rear tetraploid Sydney rock oyster larvae through metamorphosis to spat.
3. To establish of one or more breeding lines of tetraploid Sydney rock oysters. These tetraploid (4n) oysters were to be crossed with diploid (2n) oysters from an improved breeding line for the production of all triploid (3n) oysters. These triploid oysters would need to be produced by a commercial hatchery for sale to oyster farmers.

Abstract:

Four tetraploid induction techniques were tested on Sydney rock oysters Saccostrea commercialis. The first one was by blocking of both polar bodies 1 and 2 in eggs from diploids fertilised by sperm from diploids and the second one by blocking of polar body 1 in eggs from triploids fertilised by sperm from diploids. Both methods successfully produced tetraploid larvae immediately after treatment but few, if any, tetraploids survived through to metamorphosis (low levels were detected using flow cytometry). No tetraploids were detected in spat from either method when analysed by direct chromosome count. A third method, which is subject to a confidentiality agreement with Flinders University, Adelaide, was tested. This method used treatment of eggs from diploids fertilised by sperm from diploids, which again produced tetraploid larvae at day 0, but none of these survived to day 5.

A fourth method using individual electrofusion of two cell embryos produced several fusates which survived for 1 day or a little more. The experimental cell fusion technique produced small numbers of fusates per day (20-40 estimated), but the maximum production possible has yet to be determined. With the survival of Sydney rock oysters from fertilisation to 3 months old spat calculated as 5-10%, more than 400 fusates would be required to produce 20 surviving spat. This is beyond the capacity of the technique at present.