Hi, my name is Anneke and I am a postgraduate student at the University of Sydney. Please join Murray the Murray cod in learning about some of the important research that I am doing.

Today’s topic is….Iridoviruses of fish:Concerns for native fish species in the Murray-Darling Basin

© Commonwealth of Australia

Iridoviruses of fish:Concerns for native fish species in the

Murray-Darling Basin

© Commonwealth of Australia

The Murray-Darling Basin is a river system in Australia which covers one seventh of the country, making it one of the largest catchments in the world. It is home to 46 native fish species including my own species – the Murray cod.

Unfortunately in the last 50 years there has been a severe decline in the abundance and distribution of my fellow native fish species. In this presentation I am going to explain some of the reasons for this and highlight some important research that is being carried out to address this problem.

Redfin perch are the main host for a virus, EHNV which is in the Family Iridoviridae. This virus is unique to Australia and was first isolated in 1985 from redfin perch. EHNV causes sudden high mortalities of fish with the virus targeting the kidney, liver, spleen and pancreas. The virus also affects trout species, which can act as vectors to spread the disease. Experimental work has shown that a number of native fish species are susceptible to the disease.

Case study: Epizootic haematopoietic necrosis virus (EHNV)

Fish Facts: The redfin perch is an alien species widely distributed throughout the Murray-Darling Basin. Redfin perch carry disease to native fish.

The outbreak and spread of viruses that infect fish in the Murray-Darling Basin is among the key threats to native fish management in the Basin. Particular viruses of concern to native fish are known as iridoviruses.

Aquarium fish can spread disease too.….

Gouramis are the host of another iridovirus of concern to Australia, known as GIV. This virus is exotic to Australia, however in 2006 it was shown to be the cause of a mass mortality event in Murray cod – an important native fish species. Further investigation of the virus revealed that the origin of the disease was linked with the trade in live ornamental fish.

Case study: Gourami iridovirus (GIV)

Fish Facts: Thegourami is a popular aquarium fish species sold in pet shops.

Fish Facts: The Murray cod is endangered in the wild and only found in the Murray Darling Basin

Industry Fact: In Australia 18 million aquarium fish are imported annually. Despite mandatory quarantine periods imported aquarium fish have been shown to carry viruses, including iridoviruses, from other countries to Australia. This poses significant disease threats to native fish species.

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Because of the disease threats posed by iridoviruses to native fish it is important to gain a better understanding of the effect of iridoviruses which may be present in Australian waterways. The following research is being carried out as a way of addressing this problem.

Liver

Researching the development of disease in EHNV infected fish

Many diagnostic techniques have been developed to detect fish that are infected with EHNV, including immunostaining of virus particles in tissues examined microscopically. Using this method EHNV infected fish can be examined at different times of infection as a way of determining the distribution of the virus in various tissues and by examining the changes in tissue structure throughout the fish’s body. This can provide knowledge on how the virus progresses over time which is important for gaining a better understanding of the effect that iridoviruses have on native fish species.

After immunostaining examine tissues microscopically

KidneySpleen

Liver

© Commonwealth of Australia

© Commonwealth of Australia

© Commonwealth of Australia

Determining which native species can be infected with gourami iridovirus (GIV)

Although Murray cod have been shown to be highly susceptible to GIV it is not know whether any other native fish species can be infected with this virus. It is important that this information is determined as it has important implications for the management of native fish in the Murray-Darling Basin.

As the Murray cod belongs in the Family Pericichthyidae and is susceptible to GIV it is highly propable that other members of Pericichthyidae are also susceptible to the virus. As such native fish in this family, including Trout cod, Macquarie perch and Golden perch need to be tested to determine whether GIV can cause disease in these species.

Fish Facts: The Trout cod is nationally listed as an endangered species

Fish Facts: The Macquarie perch is nationally listed as an endangered species

Fish Facts: The Golden perch is listed as a vulnerable species in Victoria

So, as you can see it is important that we gain a better understanding of iridoviruses of fish in Australia, as a way of conserving native fish species living in the Murray-Darling Basin.

© Commonwealth of Australia

© Commonwealth of Australia

© Commonwealth of Australia

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This is a Anneke Rimmer

presentation for the 2009