Survey for WSSV vectors in the Moreton Bay White Spot Biosecurity Area

Project number: 2019-214
Project Status:
Completed
Budget expenditure: $64,800.00
Principal Investigator: Ben Diggles
Organisation: DigsFish Services Pty Ltd
Project start/end date: 29 Jun 2020 - 29 Dec 2020
Contact:
FRDC

Need

This project was developed to document biosecurity protocols used on affected prawn farms on the Logan River in the two growing seasons since they restarted following shut down after the 2016-17 WSD incursion. Opportunistic sampling of non-commercial crustaceans (plankton, small crustaceans) was also undertaken in northern Moreton Bay and the Logan River during April and May 2020 at a time when it was known that WSSV was active in the environment. These samples have been archived and a stop work stage of the project has been enacted upon completion of this fieldwork.

If required, the samples collected can be tested by qPCR for WSSV in order to determine if they were acting as WSSV vectors and/or reservoirs in the Logan River and northern Moreton Bay. This information would be useful to inform the design of more detailed epidemiological studies of the distribution of WSSV in the environment of SE QLD that may be undertaken in the future. Review of the biosecurity protocols the prawn aquaculture industry in the region have implemented since 2016-17 to exclude WSSV vectors from their farms will also be undertaken to determine what worked, and what didn't. This information can then be used to inform biosecurity planning for the prawn farming industry on the Logan River moving forward to identify best practice for WSSV exclusion, in order to increase their chances of successfully farming prawns in the presence of the virus and reduce risk of WSSV spillback into wild crustacean fisheries.

Objectives

1. Interview prawn farmers and collect and archive field samples of potential WSSV vectors (microcrustaceans, small crabs, plankton)
2. After approval to conduct testing is obtained, testing of vector samples at BSL by qPCR to determine their WSSV status. Examine sub-samples of populations of any WSSV positive vector species using histopathology to determine if the presence of the virus is accompanied by pathological lesions or WSD disease.
3. Development of a report which combines the results of the vector testing with the outcomes of the onfarm biosecurity assessment to arrive at better understanding of how WSSV may be persisting in the environment of SE QLD, how the virus may be gaining entry into prawn farms on the Logan River, and how to improve prawn farm biosecurity to reduce risk of WSD outbreaks on prawn farms and WSSV spillback into wild fisheries.

Final report

ISBN: 978-0-9806995-5-5
Author: Ben Diggles
Final Report • 2020-10-29 • 5.92 MB
2019-214-DLD.pdf

Summary

The objective of this project was to undertake opportunistic plankton sampling and collect small non-commercial species of decapod crustaceans in northern Moreton Bay and near the intakes of the three prawn farms which remained operating on the Logan River during April and May 2020, at a time when it was known that WSSV was active in the environment. These samples were tested by qPCR for WSSV in order to determine if these taxa were acting as WSSV vectors and/or reservoirs and to inform the design of more detailed epidemiological studies of WSSV in the environment of South East Queensland (SE QLD) that may be undertaken in the future. Interviews with prawn farmers operating on the Logan River were also conducted to document the biosecurity protocols used on affected prawn farms during the two growing seasons since they restarted following fallowing after the 2016-17 WSD incursion.
 
A range of wild taxa sampled near or on prawn farms on the Logan River were found to be qPCR positive (Ct 36.00,
 
A significant risk factor for all farms appeared to be intake of water from the Logan River after a large rainfall event in February 2020. As WSSV was found at low levels in a broad range of taxa, and at high levels in some wild prawns and crabs near prawn farms, this suggests that WSSV has become embedded in the lower trophic levels of aquatic food chains in northern Moreton Bay and on the Logan River. The virus is therefore likely to remain in this region for the foreseeable future, signalling an urgent need for prawn farmers to further increase biosecurity as they farm in the presence of the virus. As long as the White Spot Biosecurity Area remains in place, the economic impact on the commercial bait prawn and baitworm fisheries in Moreton Bay will continue to accumulate over time, potentially exceeding that experienced by the prawn farming industry

Related research

Industry
Industry
Industry

Water treatment to control influent water biosecurity risk on Australian prawn farms. Effectiveness and impacts on production ponds.

Project number: 2017-238
Project Status:
Completed
Budget expenditure: $159,800.00
Principal Investigator: David Mann
Organisation: Department of Primary Industries (QLD)
Project start/end date: 28 Jun 2018 - 28 May 2020
Contact:
FRDC

Need

The prawn aquaculture industry is committed to a strategy of enhanced farm biosecurity to reduce the potential for production losses caused by disease agents. This has been brought to the forefront of development priorities for industry by the recent white spot virus incursion into southern Queensland, but it is also driven by considerations that current farming practices are vulnerable to other disease agents that could emerge in the future. It is well recognised by aquaculture disease experts and the industry that a critical pathway for disease incursion is via the water sourced from local waterways which for Australian prawn farms is the adjacent estuarine creek or river. Treatment of farm influent water to eliminate or reduce disease agent load, particularly that associated with live vectors of disease, such as crustaceans or fish, is seen as the most basic course of action to address farm exposure to this risk.

In consultation with local and international technical experts, industry has identified that filtration and some type of chemical disinfection is the most practical approach for prawn grow-out farms. However the level of information available on design criteria and effectiveness of proposed treatment systems is lacking, particularly in relation to Australian farming conditions. Information derived from overseas experiences of farming prawns under threat of multiple diseases has been instructive, but due to significant differences in farming systems, the local industry sees a need to generate additional information that has direct relevance to Australian farms and practices. Given the anticipated high investment by farms to implement significant upgrades to water treatment practices, improved information for systems design parameters and relative risk reductions for different options under consideration are a high priority.

Objectives

1. Provide the Australian prawn farming industry with robust locally-generated information for practical farm influent-water treatment methods essential for optimising biosecurity investment.
2. Assessment of the impact farm influent water filtration and oxidative disinfection has on the plankton blooms in prawn production ponds and their management.
3. Evaluation of the capacity for influent water filtration over a range of mesh apertures to reduce the presumptive risk of WSSV transmission onto prawn farms via plankton vectors.

Final report

ISBN: 978-0-7345-0469-2
Authors: David Mann Paul Palmer Stephen Wesche Tom Gallagher
Final Report • 2021-05-01 • 5.42 MB
2017-238-DLD.pdf

Summary

This project assessed the performance of mechanical filtration as a means by which Australian prawn farmers could lower the risk of disease agent transfer into farms by selective removal of disease hosts and other vectors naturally present in farm source water. The project sought to provide technical detail for the effectiveness of water filtration options to control the risk of disease incursions and investigated the impacts of water treatment on production pond dynamics and productivity.  This report provides a number of recommendation that relate to design and operation of rotating drum filters that are considered important to achieving a high level of influent water biosecurity when implementing a single pass filtration on commercial prawn farms.