One of the major problems facing the Pacific oyster industry throughout southern Australia is minimizing the impacts to the animals resulting from general farming activities such as grading and transportation and the processing before oysters are sold at the market. A few factors have been suggested to be associated with the impacts. However, these predisposing factors for the loss of stocks can not be distinguished simply because the methods, which can be used to measure the physical changes of the stressed animals, have not been available.
If the method developed by Locoste et al (2001) for determining the haemolymph catecholamine levels in oysters can be confirmed as suitable for use in the South Australian environment using the facilities at SARDI, the suspected predisposing factors – temperature, grading, transportation, disease infection, the combinations of these factors, etc, for the stock losses in Australia, can then be identified. The performance of the oysters can then be improved by adopting the best techniques and equipment currently used by the farms and processors or by developing new farming technologies which take into account the physiological requirements of the animals. The methods and equipment currently used by oyster farms and processors have been developed mainly because of their convenience to the farmers, cost effectiveness and the ecological requirement of the animals, not because they optimise the quantity of the product.
Another limitation to the oyster industry at present is a lack of stock which have been genetically selected to produce stress-resistant characteristics. This is simply because the selection criteria can not be determined. Therefore, the project could also provide opportunities for such breeding objectives to be included in the current selective breeding program.
As a result of the development of a protocol for oyster blood sample collection, preservation and transportation and subsequent catecholamine analysis during the course of this project, a test now exists which can be used to measure stress in oysters. This test will be used in the FRDC project 2003/208 ‘Reduction in Pacific oyster mortality by improving farming and processing technologies in South Australia’ to measure the stress induced by different oyster farming practices. Based on the results from these investigations recommendations will be made to industry regarding low stress practices/technologies that may help minimise death of oysters on farms due to stress related aetiology. In addition, the stress measurement tool developed in this project could be used to improve the efficiency of selective breeding programs.
Keywords: Pacific oyster, Crassostrea gigas, farming practices, stress, catecholamines, noradrenaline, dopamine.