Megalocytivirus
In 2003 there was an outbreak of iridovirus in farmed Murray cod in Victoria that caused 90% losses. In 2004 these viruses were found in imported ornamental fish - gourami. These have established breeding populations in the wild in Australia and therefore may pose a threat to biodiversity in the Murray-Darling Basin and other systems in which Maccullochella sp. still exist. These viruses are not host specific and all Murray-Darling Basin sp. may be susceptible. Due to the risk to aquaculture, recreational fisheries and biodiversity, there is need to develop and validate diagnostic tests for GIV in order to enable rapid accurate detection of GIV, facilitate surveys of Murray cod and imported ornamental fish to improve risk assessment and conduct surveys of free-living and farmed fish in Australia. The specific tests required include a robust and accurate PCR, and cell culture. These tests need to be able to distinguish GIV from related iridoviruses such as RSIV.

CyHV-2 of goldfish
In the last 10 years imported goldfish numbers have continued to grow, in part, due to their competitive price. The imported goldfish have been subjected to the AQIS requirements for import certification and a 3 week holding period before release. Anecdotal evidence suggests that mortality rates of domestically produced goldfish increase when these fish are mixed in retail shops with imported goldfish. Investigations have revealed pathology consistent with CyHV-2. Imported goldfish may carry latent CyHV-2 infections. This project aims to provide the diagnostic capability and a sampling regime to further investigate these concerns.

The project relates directly to Strategies 1, 2 and 3 in Aquaplan 2005-2010 and meets key research area 7.2.1 in the FRDC Aquatic Animal Health Sub Program Research and Development Plan 2002-2008 (updated June 2005).

Currently there are about 180 licensed silver perch growers in all states; however, only about a third of these are producing fish commercially. Although a small number of farms achieve high production rates, most farms are inefficient and not producing anywhere near their potential. Survival, growth and production rates are much lower, and FCR's higher than achievable with good husbandry and management. Fish are being lost from disease and poor water quality, and growth rates are perceived by some farmers to be "slow".

Consultation with industry has identified that research into winter diseases and health management is a high R&D priority.

Diseases, in particular those caused by infectious agents, are recognised as an important threat to the viability of finfish aquaculture. In 1996/97 a pilot monitoring program aimed at identifying diseases causing significant production losses in silver perch was conducted on a coastal zone farm in north-eastern NSW. Results suggested that growth rates were reduced by ecto-parasitic infestations and by adverse water quality conditions. More recently, in 1998 and 1999, there have been reports of serious disease problems that have caused significant losses on some silver perch farms. These have included regular outbreaks of fungal diseases during winter, particularly in the cooler, inland areas of eastern Australia. It appears that some, or most of these outbreaks are not just the result of poor husbandry. The fungal disease, winter saprolegniosis is a serious problem in the large channel catfish industry in the USA, and relatively new winter fungal diseases have been reported in freshwater fishes in other parts of the world. There is strong evidence of a similar, but currently undescribed winter fungal disease in silver perch. Clearly there is a need to describe the major diseases, including important emerging diseases, on silver perch farms and identify their causes. Cost-effective control and prevention measures can then be developed.

More broadly, as the industry matures, silver perch farmers are becoming increasingly aware of the importance of systematic, cost-effective measures aimed at reducing disease-related losses to acceptable levels. However, no such validated programs are currently available to the industry. To fill this vacuum, it is essential that "Health Management Programs" i.e. generic disease control and prevention programs, are developed, validated and extended to farmers. These programs can be modified to suit the needs of individual farms and integrated with routine management activities. On individual farms, the programs will comprise (a) broadly targeted measures based on established principles and aimed at general disease prevention, early detection and control, with (b) specifically targeted measures aimed at reducing losses caused by important diseases (e.g. winter diseases) occurring in the farm's geographic area.

The production capacity of silver perch (10 tonnes/ha/year), the established culture techniques, the large number of inefficient farms, and the ready availability of sites provide the basis for a dramatic increase in production of silver perch over the next 5 to 10 years. However, research to address the current disease problems is required to maximise the value of previous research and to enable the industry to realise its full potential.