Project number: 2011-761
Project Status:
Completed
Budget expenditure: $113,712.89
Principal Investigator: Melony J. Sellars
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 31 Dec 2011 - 27 Feb 2014
Contact:
FRDC

Need

Outbreaks of viral disease accompanied by morbidity and mortalities occur sporadically in Australian prawn farms and are generally worst when environmental conditions are less favourable, as in the recent 2010/2011 grow-out season. Poor survival and poor market quality caused by viral disease can impact significantly on farm productivity and even the larger and more sophisticated operations are vulnerable. As the Australian industry moves towards the use of domesticated lines of genetically improved prawn species, there is an increasing need for a method capable of clearing or markedly reducing viral infection loads from valuable broodstock, thus minimizing the risks of infection being passed to progeny, either as part of breeding programs or for commercial production. Similarly, as the infection prevalence of viruses can be high amongst wild-caught broodstock still used in most hatcheries, an easy and commercially-applicable method for clearing or reducing viral infection loads would have broad industry value. In the case of Australian farmed P. monodon, GAV has the highest economic impact of known viral pathogens whilst for Australian farmed Banana prawns (Penaeus merguiensis), it is Hepatopancreatic-parvovirus (HPV). This project will therefore optimise RNAi methods to clear GAV from P. monodon whilst also producing putative RNAi reagents suitable for accomplishing the same with the Australian strain of HPV for future use in P. merguiensis. The HPV-specific dsRNAs generated will be used in this project as non-GAV non-specific controls during optimisation of dsRNAs targeted specifically at GAV.As mentioned earlier, the industry value of this project is demonstrated by the strong letter of support from the APFA attached to this application.

Objectives

1. A suite of dsRNAs targeted to GAV
2. Knowledge of the efficacy of muscle injection of the dsRNA suite in clearing or reducing GAV infection loads in P. monodon with chronic GAV infection
3. Knowledge of the spawning performance of P. monodon broodstock in which GAV infection loads have been reduced or cleared using the RNAi strategy

Final report

ISBN: 978-1-4863-0375-5
Authors: Dr Melony J. Sellars Dr Jeff A. Cowley Ms Min Rao
Final Report • 2013-12-01
2011-761-DLD.pdf

Summary

Economic losses due to diseases mostly caused by viruses remain a major obstacle to realizing the production potential of prawn aquaculture industries in many parts of the world. Broodstock used in prawn hatcheries in Australia are generally managed quite intensively and numbers used are generally low. Opportunities thus exist to inject broodstock with virus-specific dsRNAs to induce RNAi responses that reduce viral infection loads prior to them being mated and/or spawned to generate seedstock.

In Australia, disease caused by Gill-Associated Virus (GAV) infection results in the most substantial economic impacts to Banana Prawn farmers. Hepatopancreatic-parvovirus (HPV) or more recently named Penaeus merguiensis densovirus (PmergDNV) are the most problematic virus. This project aimed to optimise RNAi methods for clearing or reducing GAV infection loads in P. monodon broodstock and to produce RNAi reagents targeted to PmergDNV.

Juvenile P. monodon with subclinical GAV infections were collected from a farm in North Queensland and injected with different dsRNAs and infection loads in individuals were tracked. Reproductive assessment of egg and nauplii numbers and hatch rates showed that spawning performance of the females was not impaired by dsRNA injection.

This study demonstrated that the targeted injection of a cocktail of 5 GAV dsRNAs or a single dsRNA can reduce pre-existing infection loads in juvenile P. monodon. Similarly, the injection of a cocktail of 5 GAV dsRNAs in broodstock prawns appeared to reduce pre-existing infection loads without any adverse impacts on the ability of females to produce viable nauplii. This experiment provided the first evidence that an RNAi approach applied in hatcheries might be able to contribute to mitigation viral disease impacts in prawn aquaculture that are vertically transmitted to improve farm productivity.

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