Pearl production accounts for more than half the value of the combined Australia aquaculture industries, yet little was understood of their health status prior to project no 94/79.

There is no text available which describes, the anatomy and histopathologically of the pearl oyster, Pinctada maxima , or the histopathological changes that occur with disease. This lack of published data is compounded by the fact that there are currently only 4 pathologists in Australia with significant experience and knowledge to interpret histology sections from pearl oysters.

The publication of the histopathology photographs collected during project no 94/79 plus other reference material collected by previous researchers will help to overcome this problem.

The ability to be able to recognise what is normal or abnormal is critical in the interpretation of histology sections and hence will affect the quality of diagnostic services that can be provided to the pearling industry.

The publication of this material will also act as a reference book for a range of other investigations into pearl oysters, such as, nutritional, husbandry and biology studies. It will ensure that the material gathered during project no 94/79 will be preserved for the future benefit of the pearling industry.

Genetic variation
The results we have obtained in the current project are encouraging for SALTAS, as they confirm the earlier allozyme results of little loss of genetic variation. However, the results are also suggestive of a potential long term trend in loss of genetic variation. A sample collected and analysed in January 1997 (1993 year-class parents) would provide evidence to substantiate this trend or indicate whether the current results were a sampling artifact. The analysis of a 1997 sample would be the second of a proposed regular 4 to 5 year assessment of the status of the Tasmanian stock, and would help to describe the nature and speed of any long term trends.

SALTAS, as the principal Atlantic salmon hatchery in Australia, has a long term requirement to maintain industry and investor confidence in their product, and the ability to confirm the reliability of its breeding practices is important for the sustainability of the industry.

Loss of genetic variation in a cultured population will provide an early indicator of potential inbreeding, which could have grave consequences as deleterious recessive genes are exposed and stocks lose vigour dependent on genetic variance. Any loss of genetic variation in Tasmanian Atlantic salmon could be difficult or impossible to recover due to the restrictions on importation of new broodstock.

Y-chromosome marker
A number of molecular genetic techniques for trait or marker screening have been developed since the original proposal was submitted. We propose to apply some of these new techniques to the screening of Atlantic salmon DNA for a potential Y-chromosome marker. These approaches will greatly increase our chances of finding such a marker.

The new techniques we propose include:
Representational Difference Analysis (RDA);
PCR-Select cDNA Subtraction Technique;
the application of other modified subtractive hybridization and differential display techniques
that have proved useful in other species;
AFLP (amplified fragment polymorphism) technique; and
the application of a number of commercial RAPD (random amplified polymorphic DNA)
primers.

We have also established contact, and will collaborate during the proposed project extension, with workers who have a Y-chromosome marker for brook trout and arctic char, and other workers in this field working with other teleosts.

We believe that a continuation of the current project (95/80) is the best approach to further tackle this Y-chromosome marker issue. It will allow us to best utilise the expertise and momentum we have established on this problem, rather than completed our current objectives and then revisit this issue in a year or two.

If we are successful in locating a Y-chromosome marker either during the remainder of the current schedule or early in the 1997 grant extension, resources will then be directed to isolate and further characterize that marker.