FISH HEALTH, BIOSECURITY AND WELFARE
Since the salmon aquaculture industry began, Atlantic salmon health and performance has been a key research area for aquaculture experts in Tasmania. The aim is to provide targeted scientific support to assist the salmon industry and government in building farming practices that will have long-term environmental and economic sustainability.
Researchers in this space focus on diseases and disease diagnosis, pathogen detection, biosecurity, toxicology, and production-specific research. This includes improving nutrition and fish performance through sustainable (and local) feed production, selective breeding, alternate species, new technology, seal interactions and optimising ecosystem use.
MAIN RESEARCH THEMES AND OBJECTIVES:
- Disease and health monitoring, especially amoebic gill disease (AGD)
- Feed development and optimisation
- Disease diagnostics and vaccines through the Centre for Aquatic Animal Health and Vaccines
- Climate change effects on salmon
The topics below provide more information on research into farmed Atlantic salmon diseases, vaccine development and treatments, immune response, and understanding how a disease behaves in fish through microscopic examination of tissue (histopathology).
AMOEBIC GILL DISEASE
Amoebic gill disease (AGD) has impacted Tasmanian aquaculture stock since the mid-1980s and costs the industry AUD 40 million a year. This is because the most efficient treatment involves fish being regularly treated with fresh water throughout the marine growing cycle, which significantly increases production costs.
AGD is caused by a parasite that attaches to a fish’s gills, then accumulates and impedes the activity of the gills. This results in lower growth rates and, if not treated, even death.
IMAS has conducted research into AGD for over 30 years, with researchers identifying, characterising and naming the causative amoebic agent Neoparamoeba perurans which occurs naturally in Tasmanian waters. While the industry now uses freshwater bathing to control AGD and treat affected Atlantic salmon, research continues to seek alternative mitigation strategies.
CSIRO is working with Atlantic salmon growers to protect their fish from AGD, with one study finding that a diversity of parasites colonise the gills of AGD-affected farmed Atlantic salmon. The parasite Neoparamoeba perurans was found to correlate the most with reduced gill health.
CSIRO also developed ways to combat AGD such as breeding resistance, as well as a gill score for AGD which is commonly used by industry to help with stock management. Scientists have also looked at Brown Trout, a close relative of Atlantic salmon, to examine the mechanisms that make other salmonoids resistant to the amoeba. This work has helped to improve the health of Atlantic salmon by increasing AGD resistance by more than 35%.
SALMON ORTHOMYXOVIRAL NECROSIS
A more recent disease affecting farmed Atlantic salmon is salmon orthomyxoviral necrosis (SON), which can affect the heart, liver and kidneys of salmon. It is caused by pilchard orthomyxovirus (POMV) and is transferred from pilchards to Atlantic salmon, and can cause disease and even death. There is currently no evidence that this pathogen affects wild fish.
The Centre for Aquatic Animal Health and Vaccines has developed vaccines to control viruses relevant to the Tasmanian Atlantic Salmon industry, including for salmon orthomyxoviral necrosis (SON), Vibriosis and Yersinosis.
The Centre provides aquatic animal disease surveillance, health testing and disease diagnosis, as well as research to develop and test vaccines, and develop responsive fish health diagnostic capabilities.
It is part of the Department of Natural Resources and Environment Tasmania (NRE Tas), and is a collaborative venture between the Tasmanian Government, the Tasmanian Salmonid Growers Association (TSGA) and FRDC.
Biosecurity is the procedures or measures taken to protect people, industries and the environment from the negative impacts of pests and diseases. Inadequate biosecurity measures are a significant threat to industry, with the potential to decimate production and prevent growth.
In 2018, an FRDC-funded project assessed the level of biosecurity knowledge in national aquaculture industries, and the biosecurity practices being used in each sector. It also attempted to identify the specific needs of each sector, to support industry in developing and implementing enterprise-level biosecurity plans.
CSIRO is also working on methods to effectively identify biosecurity threats to farmed Atlantic salmon. These include sensors that monitor physiological data, as well as responses to minimise the identified threats such as selectively-bred disease resistant animals.
At the Experimental Aquaculture Facility (EAF) at IMAS Taroona, biosecurity research is conducted on a range of fish sizes through an EAF partnership with Huon Aquaculture and aquafeed manufacturer Skretting Australia. This ensures rapid industry uptake of research findings.
The EAF also has the capacity to undertake AGD research, in conjunction with these sub-optimum environmental conditions. To explore the effects of moving salmon farming off-shore, the EAF facilities can be modified to focus on swimming, respiration and energy expenditure.
Nutrition and performance are key elements of any animal domestication process, and have been essential to ensuring the economic, social and environmental sustainability of Atlantic salmon aquaculture in Tasmania.
Atlantic salmon nutrition research focuses on delivering the required nutrients for fish to grow – from different diets as fish go through various life stages and environments, to supplying specific nutrients for different times of year. As the industry became aware of issues in the supply and sustainability of products used to manufacture feeds, research has also investigated alternative sources of protein and omega oils.
IMAS conducts Atlantic salmon nutrition and performance research at the Experimental Aquaculture Facility (EAF) at Taroona. Here researchers address issues in fish performance, i.e. how efficiently Atlantic salmon grow. This involves
- optimising performance through water temperature fish feed quality and nutrition
- studying the impacts of these factors on reproductive physiology and premature maturation.
The EAF can be modified to assess the combined influences of sub-optimum elevated temperature and sub-optimum decreased dissolved oxygen, to build knowledge around how climate change affects water quality.
Tasmanian researchers conducted some of the first research in the world on the interactions between nutrition and negative environmental effects caused by climate change. This work was extended to consider impacts on product quality, such as fatty acid profile and colour.
CSIRO research includes investigating:
- how variable oxygen conditions can potentially impact the development, growth and survival of Atlantic salmon – supported by the Tasmanian salmon hatchery enterprise SALTAS
- omega-3 canola oil as a safe dietary source of docosahexaenoic acid (DHA) in salmon feed
- growth, pigmentation and plasma biochemistry of farmed Atlantic salmon
- the genes involved in Atlantic salmon maturation
Capturing an animal’s most favourable genes is vital for their successful domestication and production, whether it is selecting for growth or other traits like meat or flesh quality.
With Atlantic salmon, the early traits selected in breeding programs were high growth rates and increased resistance to amoebic gill disease (AGD). In recent times, the industry has been planning for warmer average temperatures in most areas of Tasmania, so fish are also being selected for temperature tolerance.
Warmer temperatures mean that Atlantic salmon can grow to a harvestable size within 16–18 months – but faster growth comes at a cost. While it is a benefit in the natural environment, early maturing in an aquaculture environment can cause major problems. This includes decreased growth and feed conversion efficiency, reduced product quality, and increased susceptibility to disease that can result in significant stock losses.
To address these issues, CSIRO embarked on a 7-year selective breeding project in 2004 with Salmon Enterprises of Tasmania (SALTAS). The aim: to further expand the salmon breeding industry and reduce costs, by improving fish health, warmer water tolerances, seawater growth rates, disease resistance, maturation rates, and fillet colour and oil content.
With genomic selection, growth rates of Atlantic salmon stock were increased by more than 35%, generating an estimated impact value of almost AUD 170 million. Project reports are available on the CSIRO website along with more information about CSIRO’s selective breeding research.
Tasmania is considered to be hotspot for climate change, particularly in marine environments. Back in 2008, IMAS (then called the Tasmanian Aquaculture and Fisheries Institute) and CSIRO researchers documented the impacts of climate change on Atlantic salmon farming and scoped out possible solutions for industry to adapt to these changes.
Without adaptation, increased water temperatures are likely to decrease Atlantic salmon production due to increases in thermal stress and disease events, as well as decreases in feed intake and growth. The industry currently addresses these issues through changes to farm management practices, site locations and selective breeding. How large Atlantic salmon perform in cages is another area to address.
In an FRDC-funded aquaculture nutrition subprogram in 2008, IMAS assessed the interaction between nutrition and climate change effects, particularly water temperature and associated sub-optimum conditions. This study and ongoing IMAS research has informed international models on salmon growth, redefined nutrient requirements, identified nutrition-health-environment interactions, and investigated how temperature affects flesh quality and therefore the value of salmon to human nutrition.
IMAS research shows that an increase in salmon’s protein requirements (therefore amino acid requirements) coincides with increasing temperature and decreasing dissolved oxygen. It also indicates that increased temperature will decrease essential omega-3 fatty acids in salmon. IMAS-led research has also shown that critical climate change responses may differ in individual fish according to size, sex, and ploidy, i.e. the number of chromosome sets in a cell.
