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.
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!
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.
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.
When farmed fish escape into the wild, they do all sorts of damage to native populations, such as narrowing the gene pool through inter-breeding and spreading diseases. A new study led by Melbourne Uni marine biologist Tim Dempster shows that trying to recapture escapees around marine fish farms is a bad solution that can do much damage with little good. Instead, the study suggests a radical change in focus to reduce the impacts of escapees in the wild.
There are lots of places in the world where humans put food into the ocean, either accidently or on purpose. It ends up in the mouths of animals, and can have unintended consequences. Aquaculture is a major source of this food, and feeds from aquaculture are a lot different to a natural diet.
Camille White, a UniMelb PhD student has been looking into this issue. In a paper published today, she shows how you can supersize urchins by feeding them the ‘junk food’ that spills into the environment from aquaculture, but if they get too much of a good thing, they can’t reproduce!
Big Fish by the ABC’s Four Corners program took a deep dive into the practices and sustainability of the Tasmanian salmon industry. Tim Dempster was interviewed on the conditions in 2016, the hottest summer on record in Australia for over 100 years and a challenging time for growing salmon.
Our work has recently featured in the September issue of Science News in an article on the problem of escaped fish entering the wild and what to do about them.
SMOOTH CRIMINAL Farmed sea bass and other fish frequently escape from sea cages out into the ocean. Researchers worry that escapees, like this sea bass found off the coast of Tenerife in the Canary Islands, could threaten wild ecosystems.