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‘Summer Special’ oysters.

Have you ever had a problem selling oysters in the summer ? Do they spawn in your purification tanks ? Do they go milky and your customers dislike the rich taste ? Do they sometimes spawn in the sea and then become unsellable because the meats are so thin ? If the answer to any of these questions is yes, then you probably have a good growing site but you could benefit from triploid oyster seed.

What are Summer Specials ?

Triploids are produced in the hatchery by treating the eggs, usually with a chemical, so that they retain an extra set of chromosomes and are thus rendered (almost) sterile. In all other respects they are identical to normal (‘diploid’) seed.. Although there are theoretical advantages for growth rate (since they are putting less energy into reproduction), in practice most people find they grow about the same as any other oysters. The difference is in the summer when the triploids should retain a much better meat quality - especially in rich growing areas.. This is important not just for the market, but it may help to avoid summer mortality in part-grown stock.

In the hatchery they are difficult to produce in large numbers and within each batch not all will be triploid - 70 to 90 % is the target to be acceptable in the restaurants. The grower then has the problem of keeping them separate from other stocks - easier said than done ! Then there is a potential problem with marketing when we must counter any suggestion that they are not ‘natural’. It is important to realise that triploid oysters do occur occasionally in the wild and are not ‘genetically modified’. The technique is used extensively in horticulture, and in finfish farming. Hence my suggestion ‘Summer Specials’ - does anyone have any better ideas ?

A lot of the pioneering work on triploid oysters was done in 80’s on the West coast of America where now about 50% of the commercial hatchery production is triploid. I believe Guernsey Sea Farms was the first hatchery to produce triploids in Europe in about 1990. We now have had several batches which have been through to market where they have been well received. The experience in 1995 that they survived the high summer water temperatures better has led to new interest and this year we have increased production so that nearly half our seed is triploid and now available for trials.

There is the prospect of being able to produce ‘tetraploids’ from which, when crossed with diploid, it is possible to produce 100% triploids. Guernsey Sea Farms has a collaborative project this year with MAFF Conwy, U.C.C. and American researchers working on this.

We see triploids as important to the development of our business as a specialist hatchery. They should also fit well in an Irish market which should be increasingly aiming to distinguish its product on the basis of quality. It may be hard to keep the stock separate on the shore but, for many areas, it should be well worth the effort.

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