Know your enemy – understanding the movements of a devastating parasite to outsmart it

Sun Tzu’s ‘The Art of War’ tells us we must know our enemy if we hope to defeat it. In modern aquaculture, the greatest enemies are parasites that plague production and are a key part of many environmental effects. One of the worst parasites in salmon farming is a pesky amoeba that causes severe gill damage. As parasite outbreaks are extremely costly, the search is on for methods to reduce infection rates. One strategy is to reduce contact between salmon and the parasites in fish farms. But to do this, we must first know where these tiny parasites are and what drive their movements.

In a new study published in Aquaculture Environment Interactions this month, Dr Daniel Wright and colleagues from the University of Melbourne hunted for this marine parasite in Tasmanian salmon farms over 2 years. After taking over 300 separate water samples at farms and in their surrounds, there was no clear pattern between where the parasite was, depth in the ocean or the swimming depth of the fish.

Now we know our enemy, we have a better idea of which control methods will work and which won’t. For other parasites, control methods we developed that permanently change the swimming depth of fish swim are very successful. But they won’t work for this amoeba. We must now look for other possibilities to disconnect amoeba from salmon. These could include spreading fish densities more evenly at night with underwater lights and moving fish into brackish water that makes the amoeba leave the gills.


Rapid growth leads to hearing loss in farmed salmon

A new article led by Tormey Reimer, a Melbourne University Masters graduate, reveals that about half of farmed salmon are deaf due to accelerated growth in the aquaculture industry. Tormey and colleagues discovered that fast-growing fish were three times more likely to have ear bone deformities, leading to substantial hearing loss.
In this pursuit article, co-author Associate Professor Tim Dempster explains that these results “raise serious questions about the welfare of farmed fish” as the deformity is irreversible and becomes worse over time.

Earbones from the same farmed Atlantic salmon. The left is normal, while the right has 90 per cent vaterite deformation. Picture: Tormey Reimer

Escapes from aquaculture – what a technical standard can do

The recent dramatic images of the breakdown of an Atlantic salmon farm on the Pacific coast of the U.S. are startling. Square steel cages in a tangled mess with the fate of the 305000 fish they contained as yet uncertain. Some have been recovered from the cages, some will have escaped. Norway suffered a similar spate of escapes due to whole cage or farm breakdown over a decade ago. Norway still suffers escapes from salmon farms, but farm or whole cage breakdown has disappeared from the causes of escape. How did they fix it?

From 2009-2012, the European Union’s Prevent Escape project led by Tim Dempster (now with the Sustainable Aquaculture Laboratory at the University of Melbourne) delved deep into the causes and consequences of escapes from aquaculture, with the purpose of identifying how we could better stop escapes.

As part of the project’s work, a detailed analysis of escapes in Norway’s Atlantic salmon production revealed that after the Norwegian technical standard (NS 9415) for the proper design, dimensioning and operation of sea-cage farms was implemented in 2006, the total number of reported escaped Atlantic salmon declined dramatically, despite the total number of salmon held in sea-cages increasing by greater than 50% during this period (Jensen, Dempster et al. 2010; Aquaculture Environment Interactions).

What did the introduction of the technical standard do? Well, it encodes the type of technology (cages, mooring systems etc.) that can be used at farming sites depending upon the maximum forces those sites experience in a once-in-50-year storm or severe weather event. Prior to the technical standards introduction in Norway, big escapes happened due to the breakdown of cage structures and mooring systems. The technical standard basically eliminated complete farm failure as a cause of escape.

Based on the success of this measure, the Prevent Escape project recommended that policy-makers worldwide introduce a technical standard for sea-cage aquaculture equipment coupled with an independent mechanism to enforce the standard. We were pleased to see that Scotland followed with a new technical standard in 2015, yet other producing nations are still lagging behind on this key mechanism to prevent escapes.

It leads us to ask the question, if the U.S. had introduced a legislated technical standard that reflected best practice and drew upon the long success of the Norwegian technical standard, would this massive escape ever have occurred?

PhD project with $10000 per year top-up scholarship available

The future of aquaculture: how will fish cope with an offshore life?

A PhD project is available to investigate the behaviour and welfare of farmed salmon in new and emerging fish farm designs, principally for offshore and exposed locations. The project is a collaboration between the Sustainable Aquaculture Lab at the University of Melbourne ( and the Institute of Marine Research, Norway ( The student will be based in the School of BioSciences at the University of Melbourne, while experimental work will occur at the Institute of Marine Research’s state-of-the-art aquaculture research facility near Bergen, Norway, and in the field at commercial farms around the scenic fjords of western Norway.

There has been much debate regarding the salmon industry’s footprint in coastal waters. Part of the debate has revolved around whether farms should move to more exposed or offshore locations, where many of the problematic interactions with coastal environments and communities might diminish. A myriad of new fish farming concepts are now being proposed and implemented to tackle this challenge.

Offshore and exposed production system types have design aspects that alter the environmental conditions and behavioural context for fish relative to standard farms. Understanding these new production environments and their challenges for fish is key to success. Existing evidence suggests that several parameters critical for production will differ, including current flows, fish swimming speeds, school structure, dissolved oxygen levels, and fish buoyancy levels.

The PhD project will develop knowledge of the behaviour and welfare of salmon in new production systems. We will use a range of equipment to study fish farming environments and fish behaviours, including individual fish tags, echo sounders, and camera systems. Experiments will be conducted in research facilities and salmon farms that are testing new technologies.

The student will need to obtain an Australian Government Research Training Program Scholarship (…) for a PhD at the University of Melbourne. A first class honours or Masters is essential to qualify. A $10 000 per year top-up scholarship will be available in addition. Experience working with fish or in marine environments is desirable, but not essential. The student must be prepared to spend 2-3 months per year in Norway for experiments. The project starting date is flexible.

Expressions of interest (with CV attached) are welcome at any time until the position is filled. For further information contact Assoc. Prof. Tim Dempster (

Can we “program” fish by modifying their environment during early development to improve performance?

Salmon farmers want fish to be healthier, faster growing and to produce flesh of the highest quality at harvest. Unlike livestock, fish spawn eggs into the water, so that eggs, alevin and other stages of early development are fully exposed to a range of different factors which occur in the natural or aquaculture environment. A number of important processes and systems develop and become functional during these early stages of development (eg. the immune system, musculature, stress response axis etc).

We know that some external factors, like water temperature, can affect these developmental processes (for instance, higher temperatures resulting in higher incidences of spinal and jaw deformities). Some such factors are known to change the “epigenome”, areas outside of the genome that can have lasting affects throughout development on the rate of gene transcription. But what if we could manipulate the environment in which the animal is immersed to optimise and tailor development to produce a faster growing, healthier fish of exceptional quality?

In a new paper published in Scientific Reports, a team of Scientists from Nofima in Norway, including Associate Professor Nick Robinson from Melbourne University, have investigated how low temperatures and oxygen deprivation can program the Atlantic salmon embryo and post-hatch larvae to affect performance of the fish in later life. Low temperature and oxygen deprivation during these developmental phases were found to modify the epigenome, so that gene expression was regulated in a way that affected the subsequent growth performance of fish for 35 days after they were put out to the sea in cages. Fish that were treated with such mild chronic stresses both during embryonic and post-hatch larvae stages grew faster than unstressed fish, or fish that were treated at just the embryonic or just the post-hatch larvae stage.

The findings support the general notion that tighter regulation of factors in the water surrounding the fish during these early developmental phases could be utilised in a way to program the animal for improved performance in the aquaculture environment.

Supersizing fish farms – the way forwards?

There has been much debate in Tasmania regarding the salmon industry – how much farming there should be and where it should occur. Part of the debate has revolved around whether farms should move to more exposed or offshore locations, where many of the problematic interactions with coastal environments and communities might diminish.

In that context, SALTT has been closely following global innovation trends in aquaculture. There is now a distinct movement towards bigger farming units in more exposed locations to solve similar problems.

Check out this video – construction of the world’s largest fish pen, capable of holding 1.5 million salmon at harvest size (that is about 7500 tons!), built in China for a Norwegian salmon farming company.

The world will be watching how successful this new technology is and if it can crack open some of the problems current day farms face.

Swim deep and stay safe from parasites

For Australians, ‘sea lice’ are the bane of beach goers – microscopic marine irritants that get down your ‘budgie smugglers’ and leave a nasty rash. In the world of salmon aquaculture, ‘sea lice’ are an altogether different foe, tiny parasitic copepods that attach to fish and eat their skin and blood, leaving a horrifying bill of around US$2billion per year.

Earlier this year, we posted on a great new paper by Daniel Wright and colleagues about how an invention, the ‘snorkel cage’, reduced infection of farmed salmon with parasitic sea lice. The new fish farm design prevented fish from accessing parasite-risky surface waters by using a net roof and a lice-proof ‘snorkel’ tube up to the surface.

We have pushed the technology further in a new study published in Pest Management Science, written by a team led by Frode Oppedal from the Institute of Marine Research in Norway and SALTT resident fish vet Francisca Samsing at the University of Melbourne. Here, we showed that the deeper the snorkel, the better the preventative effect against sea lice, without affecting fish welfare. In the deepest snorkels, fish caught 10 times less lice than fish that swam shallow with no protection. It is terrific to see the industry taking up this new invention, with many snorkel cages now in place against these parasites.

Fish farm waste: junk-food of the sea?

When waste from aquaculture flows into the marine environment, it becomes a food source for many marine animals. While rich in energy, this food contains a high proportion of terrestrial fats and oils, which are normally alien in the diets of marine consumers. The impact that this “junk-food resource” has on the ecology of marine ecosystems is poorly understood.

In a new study, University of Melbourne PhD student Camille White and colleagues investigated consumption of aquaculture waste by the white sea urchin in Norway. Camille spent many chilly days immersed in the spectacular western fjords of Norway to pull off this research.

The white urchin is a keystone species in Norwegian fjords and has the potential to drive ecosystem level change through over-grazing on kelp and creating bare rock barrens. Camille found that urchins are generalist feeders, that supplemented their normal diet with farm waste, readily exploiting aquaculture waste as an energy-rich food source. Just what this means for the urchins and their ability to reproduce, will be published in a few months time. Stay tuned!

Camille White during fieldwork in Norway.

Infection protection with new fish farm design

Before ending up in your chopsticks or sushi roll, few people are aware that farmed salmon are commonly plagued by parasitic lice on their skin and amoebae on their gills. Fish farmers continuously struggle to control them, and the control methods themselves are often rough on the fish. An innovative new fish farm design has taken a different approach to prevent lice from infecting salmon in the first place.

Lice use light cues to aggregate in the surface layer – this behaviour is their Achilles heel which can be used against them. The new farm design has a deep net roof and a lice-proof ‘snorkel’ tube up to the surface. This surface access tube is needed as salmon use the snorkel to swallop air to re-inflate their buoyancy-controlling swim bladder. If they can’t get to the surface to do this, they are too heavy and keep sinking.

In a new paper published in Preventative Veterinary Medicine, Melbourne University PhD student Daniel Wright and colleagues document how these new snorkel farms are working at industry scale. They clearly reduce lice, but gill amoebae infections were elevated from holding fish in less space. To solve this problem, snorkels were filled with freshwater to remove the freshwater-sensitive amoebae. Danny’s work shows that farmed salmon of the future could be less burdened by these two important parasites using this new method.

Danny finished his PhD in late 2016 and moved to Norway to do a post-doc to further this exciting work. We wish him well.

Farmed salmon – mostly clueless about dissolved oxygen

Of the many factors which limit the growth and survival of farmed salmon, hypoxia (low dissolved oxygen concentration) is among the most complex to monitor and remedy.  In a new study, PhD student Tina Oldham and colleagues manipulated dissolved oxygen levels within sea cages at certain depths by the use of a tarpaulin to block the inflow of water. While caged Atlantic salmon behaviour and distribution after DO levels plummeted in this zone were partially explained by the poor oxygen conditions, other environmental factors such as temperature and salinity were far more powerful predictors of what the salmon did. These findings suggest that, in the highly variable marine cage environment, salmon are likely to expose themselves to sub-optimal oxygen conditions even when ideal conditions are available.

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