Freezing oyster eggs a world-beater

Scientists in Nelson are believed to have achieved a world first by freezing Pacific oyster eggs.

The technique, perfected by scientists at the Cawthron Institute, has major implications for the seafood industry, allowing eggs and sperm from the best shellfish stock to be preserved beyond the normal lifespan of the animal.

The scientists have been working on cryopreservation since 1998, but their findings have only just been officially published.

Cawthron's commercial manager, Mark Jarvis, said it was a first in terms of cryogenically freezing a bivalve species. It was an important find in breeding better oysters - and potentially other shellfish.

"It enables you to basically preserve generations so that you no longer rely upon individual animals surviving - which means that you can pull something out of the freezer to breed from if it had some particular characteristics that you wanted to breed into a new oyster.

"You can have a storage system for previous generations which you can breed from if you realise they have traits which become desirable.

"Although people have been breeding cows for thousands of years, in shellfish it's really only been happening for 10 years. The whole selective breeding benefits [in shellfish] have yet to be seen."

Cawthron was investigating if the method could be applied to mussels and other shellfish, said Mr Jarvis.

Programme leader Serean Adams said cryopreservation had never before been achieved with the eggs of any fish or shellfish because the freezing process kept killing the eggs.

If something was frozen too quickly, ice crystals formed and damaged the cells. Freezing too slowly also created problems, she said.

"Somewhere in between is where you can get it to survive."

The eggs could potentially be frozen for up to 1000 years, she said.

The team first reared Pacific oysters from cryopreserved eggs in 2003, but the survival rate was not high.

Developments since then have increased the survival rate to 60-70 per cent, not too far off the 90 per cent survival rate of eggs which have not been frozen, Serean Adams said.

Cawthron has applied for a patent, and since its findings were published the team has been contacted by researchers overseas.

Mr Jarvis said the patent would allow for cryopreservation expertise to be kept in New Zealand.

The knowledge could be used in other fields, such as in the conservation of endangered species.