Vaccines for Trout

The finfish disease lactococcosis, which is caused by the bacterium Lactococcus garvieae, is prevalent during summer in Australian trout farms in all states where they are farmed for the table or for restocking recreational fisheries. As L. garvieae infections are linked to warmer waters, the prevalence and impact of lactococcosis are expected to increase with climate change.

Lactococcosis has a significant economic impact on aquaculture. In summer 2022–2023, for example, the Victorian trout farms most affected by the disease experienced estimated losses of 120 T of biomass, valued at $1.5 million.

Mortality in affected populations can exceed 40% of pond populations, causing acute-onset disease in fish between 50 g and 3.5 kg. Affected farms also incur hundreds of thousands of dollars of lost growth and financial costs from the interrupted supply of product to market.

L. garvieae infections are managed by treating fish with antibiotics under veterinary prescription, combined with dramatically lowering feed rate, ensuring high levels of water oxygenation and lowering stocking density.

There are currently no effective vaccines against lactococcosis that provide long-term protection.

However, the experience of the Atlantic salmon farming industry in Tasmania suggests that vaccination providing fully protective, sustained immunity could reduce antibiotic use by more than 90%.

We will develop an effective vaccine against L. garvieae in Australian trout farms. Vaccine efficacy will be assessed through laboratory and field research. Working with field vets and industry, we will build knowledge on the factors that contribute to disease outbreaks and identify additional management measures to support vaccine prevention of disease.

To aid vaccine adoption, we will provide the information needed to manufacture and use the vaccine safely and effectively. This will include a data pack to facilitate minor-use permit approval.

Once the vaccine is in use, we will monitor its continued stewardship using a robust and reproducible L. garvieae strain typing method. We will also establish a comprehensive epidemiological dataset to monitor for the presence and spread of AMR in L. garvieae in Australian trout farms.

This data will permit the rapid reformulation of vaccines if new bacterial serotypes are detected.

Adoption of vaccination to prevent lactococcosis would substantially reduce antibiotic use and improve fish health and welfare on-farm. This will help reduce the risk of AMR developing in this major fish pathogen.

The project provides a complete pipeline, from research to vaccine adoption, by bringing together the trout industry, represented by the Fisheries Research and Development Corporation (FRDC), aquatic vets, a vaccine manufacturer, state governments, and the Australian Pesticides and Veterinary Medicines Authority.

Trout farmers, consumers

4 years

Bacterial samples from the summer 2023–2024 lactococcosis outbreak have been collected, and their DNA has been sequenced. Preliminary conditions for microbial fermentation to manufacture test vaccines have been optimised. The team has also documented and optimised the expression of major L. garvieae antigens. Epidemiological information from the 2023–2024 farm outbreak is being assembled.

The project team will develop safe and ethical clinical trials to test experimental vaccine formulations in trout at the University of Queensland.

Fisheries Research and Development Corporation (FRDC) invests in research, development and extension activities to increase economic, social and environmental benefits for Australian fishing and aquaculture and the wider community.

University of Queensland

Treidlia Biovet Pty Ltd

Future Fisheries Veterinary Services

Tasmanian Department of Natural Resources and Environment