Freshwater bathing is the go to treatment for amoebic gill disease (AGD) in many farmed fish species. Treatments are typically 2-4 hours long and kill the amoeba. This restricts how and when treatments can be delivered. Dr Daniel Wright from the SALTT lab and co-authors tested if using short, sub-lethal freshwater treatments were just as good at removing amoeba as long, lethal treatments. Sub-lethal (daily 30 min treatments) and lethal (daily 120 min treatment) treatments for 6 days both reduced amoeba compared to short daily 3 min freshwater treatments. In short, repeated sublethal freshwater treatments could be just as effective as longer, lethal doses of freshwater. Danny’s results could be transformative to the industry as they open up new ways to deliver treatments that are easier for farmers to do and less stressful for the fish.
Cryptic biodiversity in the freshwater fishes of the Kimberley endemism hotspot, northwestern Australia
The prevalence of unrecognised species is a real problem for estimating true biodiversity and hampers conservation planning. The remote and spectacular Kimberley region in northwestern Australia, with its rugged landscape and deep gorges, harbours some of the most diverse and unique animal and plant communities in Australia. Recently, many new cryptic species have been found on land, raising the question of whether the rivers and streams are also full of unrecognised species. We sampled fish from rivers right across the Kimberley and assessed different molecular genetic data for the Kimberley’s most species-rich fish family, Terapontidae. Clear evidence exists to describe 13 new fish species. Many of these new species are only found in a single river. Our findings show that the fish biodiversity in the Kimberley is severely under-represented, with significant implications for ecological research, conservation and management.
A couple of our PhD students strayed into the amazing rivers of the Kimberley region for their research. Recently they released a beautiful new book ‘Freshwater Fishes of the Kimberley’. Congratulations to James Shelley and Matthew LeFeuvre.
For those interested in a copy, they are only $20 here.
Bigger cages potentially allow for increased Atlantic salmon production and higher profitability, but only if water quality remains good. As cage size increases water exchange decreases, which may in turn cause low dissolved oxygen conditions within cages. To test this, PhD student Tina Oldham from the University of Tasmania compared how dissolved oxygen concentrations varied with cage size on a commercial salmon farm during the 2015/16 Australian summer heatwave. Overall, Tina found that dissolved oxygen levels in all tested cages were generally high and suitable for salmon feeding and growth, and lowest oxygen concentrations consistently occurred in the larger cages. Bigger, it turns out, is not always better.
Amoebic gill disease and salmon lice are among some of the greatest challenges the Norwegian Atlantic salmon farming industry faces. Manipulating surface conditions and pushing fish down beneath the surface layers with the highest infestation pressures could potentially control and prevent infestations. Dr. Daniel Wright from the Institute of Marine Research tested if a permanent freshwater surface layer in snorkel sea-cages can reduce amoebic gill disease and salmon lice levels compared to standard commercial cages. While freshwater surface layers were unable to prevent or reduce AGD and lice infestations, further research should test if other behavioural and environmental manipulations can be used to prevent parasites from infesting farmed salmon.
The use of farmed and restocked fish to supplement the worldwide human consumption of fish, recreational fishing stocks, and conservation efforts, is growing globally. But how well fish survive after release from hatcheries is still a mystery in many places. Hatcheries seldom mark or tag all fish prior to release, despite a range of mass-marking methods being available to mark farmed and restocked fish en masse. In a recent paper, Dr. Fletcher Warren-Myers and co-authors reviewed a range of thermal and chemical otolith (ear-bone) marking methods to assess their suitability as mass marking tools for hatchery-produced fish. These marking methods were compared in terms of (1) ease of application, (2) cost, (3) mark longevity, and (4) effects on fish welfare. His conclusion? Although some techniques will have limited use due to regulations, the majority of otolith mass marking techniques are simple, easy to apply, cost effective and highly suitable for long term monitoring of hatchery produced fish.
Climate change is a major threat to biodiversity and important species on our planet. A potential solution to prevent vulnerable species from being lost is improving their thermal tolerances, making them better adapted to warmer temperatures and climates. University of Melbourne Masters student Kristal Sorby and co-authors tried to improve survival of individuals to extreme heat events within and across generations using a brine shrimp (Artemia franciscana) as a test animal. In combination with serotonin, methionine or neither, brine shrimp were exposed to ‘heat hardening’ over two generations and their thermal tolerances were recorded. While treatments did not increase their upper thermal limit, serotonin and methionine-treated shrimp outperformed control shrimp for thermal performance traits. Some effects were also present across generations, suggesting that heat hardening could provide resilience and stability in populations vulnerable to increasing temperatures.
A cure should never be worse than the disease. In modern aquaculture, unfortunately that’s not always the case. When chemical treatments for parasites go wrong, they go very wrong, and cause mass mortalities of hundreds of thousands of fish.
One very common treatment to control external parasites is hydrogen peroxide baths. For salmon, the treatment is extremely toxic at warmer temperatures and can lead to fish deaths.
Kathy Overton, a Melbourne University Masters student invented a new method to make hydrogen peroxide treatment more fish friendly. By switching fish from warm ocean temperatures to cold treatment baths, Kathy showed the treatment was just as effective against the parasites and no deaths occurred. Once the industry takes up the new method, millions fewer fish will suffer each year.
Introducing Urchin Aquaculture Australia – a collaboration between The University of Melbourne, Deakin University, Southern Cross University and industry partner, AquaTrophic.
Sea urchin roe (‘uni’) is a prized delicacy in countries such as China and Japan. Uni is a particularly high value product, with a large export market in Japan worth around US $200 million annually. Increasing demand and reduced supply from collapsing wild fisheries are creating opportunities for commercial sea urchin culture in Australia to supply the Japanese market.
The aim of our AgriFutures Australia-funded research is to target major bottlenecks in sea urchin aquaculture industry development. Our current research focuses on two commercially-valuable sea urchin species: the collector urchin (Tripneustes gratilla) and the purple urchin (Heliocidaris erythrogramma).
To learn more, head to www.urchin.org.au.
A terrific article on the groundbreaking research of past PhD student Samantha Bui, which was recently published in the Journal of Zoology. Through a creative experiment, Sam and her colleagues worked out that fish have an inherent ability to use behaviour to deter parasites at the point of contact. Behaviour really is the first line of defence.
Her results are important for aquaculture – if the artificial environments fish farms create restrict the way fish display these natural defence behaviours, then they will be more susceptible to infection.
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