2011/761 Optimisation of viral clearance from broodstock prawns using targeted RNA interference

By Melony Sellars

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.