Oyster Health Sydney

Welcome to Oyster Health Sydney!

This comes to you from the Aquatic Animal Health team in the School of Veterinary Science at The University of Sydney. We are affiliated with The University of Sydney Marine Studies Institute, the Sydney Institute for Infectious Diseases and the Sydney Institute of Agriculture.  We hope you enjoy this site, the opportunity it provides to view our research, and the means it gives you to offer advice, comments and suggestions to assist our research program.

We believe that healthy oysters are central to a sustainable oyster industry, the coastal community it supports and to healthy estuaries. But how do you assess health, and what factors determine whether a healthy batch of oysters will remain healthy in the presence of disease threats? How does the environment and Australia’s biosecurity system affect oysters? How can oysters be managed to minimise the risk of losses due to infectious diseases? Can we immunise oysters? Why not just breed for disease resistance? These are some of the questions we try to answer in our multidisciplinary research program.

We work closely with oyster growers and benefit from their great insight about the best methods for oyster farming. This knowledge includes many traditional practices to avoid common diseases. Unfortunately the emergence of new diseases has increased the risks of farming oysters and this is where science must step up to meet the challenge. Quick fixes do not exist, and those who promise them must eventually produce evidence.

The Australian oyster industry faces many challenges due to climate (fire, flood and climate change) and human-associated environmental conflicts (urban estuarine pollution, agricultural runoff). Superimposed are infectious diseases like Pacific Oyster Mortality Syndrome (POMS), which is caused by a marine herpesvirus and QX disease caused by a parasite. This blog will be focussed for some time on POMS. However, the principles we use in POMS research are directly applicable to QX.

Fundamental research on the life history of infectious disease (epidemiology, using tools of microbiology, virology, parasitology, immunology and pathology) should accompany applied research on approaches such as husbandry and genetic selection so that efforts are focussed and lead to measurable outcomes rather than anecdotes. Sadly, we know exponentially more about POMS, a disease that has been present in Australia only since 2010 than we know about QX disease, which has been present for more than 50 years, due to poor research leadership on the latter.

We communicate our findings in a variety of ways, including via this website. We ensure rigorous standards in research and ensure that our findings are publicly available for assessment by industry and the international scientific community. We aim to publish in scientific journals in a timely manner to encourage uptake and independent verification of our results in other settings – please look at “Scientific Publications”. We are accessible and meet with farmers, farming associations and media. We have produced Fact Sheets that may be useful in the face of a POMS disease outbreak, to assist with disinfection, prevention of mortalities in hatcheries, and to help reduce losses and salvage value when an outbreak occurs on farm – please look at NEW:POMS Fact Sheets.

Despite progress in the husbandry of oysters, and claims about improved genetics, it is currently impossible to restock a farm with  spat in a POMS endemic area and be confident about their survival. Results from commercial trials in NSW in 2018, utilising genetically improved stock in which POMS disease events were to be monitored cannot be properly interpreted. Our own independent observations from Woolooware Bay suggest survival prospects of only 50%. Our long-term field research identified a consistent window of infection for POMS which currently enables farmers in the Hawkesbury River to manage seasonal stocking and harvest times to minimise losses. Environmental conditions, specifically low water temperatures, do favour survival in some estuaries particularly those in the south and in Tasmania in most years, but climate change will remove this advantage over time.

In a surprising development in 2022, which came about because we independently sequenced many isolates of OsHV-1, we confirmed that POMS virus did not come from known hotspots in Europe or Asia. The Australian virus is unique and it might have been present for a long time. Even more surprising was the fact that virus has not spread between the two affected estuaries in NSW nor between NSW and Tasmania – outbreaks in these locations were due to different strains of the virus. Furthermore the Australian POMS virus is not microvar (OsHV-1 uVar) despite this diagnosis being made officially in Australia 10 years ago. Please see our publications pages for the details.

What about vaccines for POMS? This idea goes against the dogma in the discipline of immunology because invertebrates are supposed to be primitive animals. However, natural immunity to POMS is obvious in oysters that have survived outbreaks – they are resistant to further exposure to OsHV-1 in the estuary, do not appear to be the source of the virus for subsequent outbreaks on farms and they survive challenge with infectious virus in the lab. Furthermore, we have proven that “vaccination” of oysters with heat-killed OsHV-1 provides protection against later challenge with virulent virus in the lab. This is proof of concept for vaccination but requires further research on delivery mechanisms and efficacy at commercial scale. Again please see our publications pages for the details.

The oyster industries require ongoing research and development for new innovations and future prosperity, but without leadership to define endemic disease research needs, better integration of breeding programs with other disease controls and appropriate resourcing and supervision of suitably qualified research teams, the default position of biosecurity crisis management during disease flare-ups will prevail.

Emeritus Professor Richard Whittington

University of Sydney,

Camden, NSW Australia

Last updated: September 2023