Nodavirus in wild barramundi populations

* There is a need to address concerns about the effect of stocking hatchery-reared barramundi on the level of unapparent nodavirus infections (that is, the prevalence) in wild barramundi.
* The first step is to determine the prevalence of nodavirus in wild populations of barramundi (that is to say the natural level of nodavirus-carrier status – an infection without disease).
* The baseline nodavirus prevalence data will permit:
- comparison of barramundi populations in areas where stocking has or has not occurred,
- assessment of changes in prevalence of nodavirus in future years,
- effective decisions about appropriate sources of replacement broodstock for breeding programs.

Nodavirus in freshwater fishes

* There is a need to address concerns about the risk of possible lethal transmission of barramundi nodavirus to freshwater fishes.
* Recent investigations have shown a possible susceptibility of freshwater fishes to barramundi nodavirus and that nodaviruses naturally occur in species other than barramundi in Australia, including the freshwater species, sleepy cod.
* There is a need to determine if there are nodaviruses in freshwater fishes as a risk analysis for translocation should include disease-status information in the receiving population.

Are the nodaviruses found in freshwater fishes related to barramundi nodavirus?

* If nodaviruses are detected in freshwater fish an analysis of relatedness (sequence analysis of PCR products) could indicate an association to previous stocking in that area of hatchery-reared barramundi. This information would support effective risk analysis for future translocation considerations.

A testing protocol for hatchery production of nodavirus-free fish fry.

* Broodstock screening protocols to identify nodavirus-free broodstock have been described from overseas but the detection tests used then are not as sensitive as the two-step or nested RT-PCR, and the protocols include a requirement for egg/water disinfection and repeat testing of larvae.
* There is a need to evaluate and validate the sensitivity of the two-step or nested RT-PCR to identify nodavirus-free broodstock and to determine if one or more tests are required to confirm the nodavirus-free status.
* There is a need to confirm in barramundi that larvae/fry become infected by nodavirus through the vertical transmission route (ie., from their parent(s)).
* There is a need to determine if fry can become infected via nodavirus-contaminated water once they are stocked into nursery systems.
* If the vertical infection route is the same for all fish species, the information on the testing protocol required to produce nodavirus-free barramundi fry will be a model testing protocol applicable to all fish species in breeding programs in Australia.

Training is needed, for fish farmers, technicians & veterinarians in all Australian States, for increased vigilance with respect to early disease detection, diagnosis, control and eradication of newly emerging endemic and exotic fish diseases. Northern States of Australia (NT, Qld) are at greatest risk for disease incursions, via the vast expanse of the States & Territories, remoteness of farms, illegal trade of fish, fish products, shipping movements (over 13 ports in Qld), people movement and the proximity of northern Australia to Indonesia, PNG and Asia. Early fish disease detection and eradication is necessary to protect the Biosecurity of the Australian Fish Farming industry, and prevent disease spread within and between States.

The continued annual growth of the barramundi & freshwater fish industries in all Australian States precipitates the need for farmer training for disease detection at the grass-roots level for farm workers to detect, control and treat fish disease, and thereby reducing disease risk to aquaculture enterprises and fisheries resources.

A specific training workshop is needed to train fish farmers, technicians, fisheries officers, vets, with hands-on, practical, technical skills & knowledge by Aquatic Animal health Professionals, so skills can be practically applied on farms during disease epizootics, investigations, and disease emergencies. This is needed to support continued growth, productivity, & sustainability of the Australian Fish farming Industry, disease being a limiting factor. This Workshop is needed to support on-going disease reporting activities by all States to DAFF, OIE and NACA, allowing continuation of Australian trade in fish and disease-free status.