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The research could finally make the treatment of sea lice effective.
The study’s results appear in the latest edition of the Journal of Animal Science.
Dr Tim Dempster from the University of Melbourne and researchers from the Institute of Marine Research in Norway were able to show that by blocking salmon from the water’s surface with a net barrier for a day and by removing it afterwards more than 90 per cent of the fish were prompted to jump several times through the surface in the following two hours.
In the 1990s, scientists pursued a de-lousing method consisting of adding a thin layer of oil containing a sea-lice treatment chemical to the water’s surface, which would coat the fish if they jumped through it. But salmon did not jump through the water’s surface frequently enough and the chemical broke down in the sunlight.
“In response to this problem, our study has demonstrated a way to induce salmon jumping behaviour so that it is frequent and predictable, therefore ensuring the surface treatment method is effective in de-lousing salmon,” Dempster explained.
“Such treatment is valuable to the industry as sea lice are one of the most significant problems for the world’s salmon farmers because they cling to the skin of salmon, feeding on mucous and blood and cause painful lesions, which lead to infections and poor growth,” he continued.
The researchers suggested that the behavioural changes may be due to salmon’s empty swim bladder - an internal air pocket that some fish use to adjust their buoyancy – which is open instead of closed, as in most fish. An open bladder can only be filled up when the fish swallow air above the water.
Unlike traditional chemical treatments for sea lice, the oil mixture is relatively environmentally friendly because it can be recollected from water after use instead of being left to dissolve in the water.
"Compared to present-day techniques, which are expensive and manual labour intensive, this method has the potential to be both cheaper and easier for farmers," Dempster said.
Meanwhile, the issue remains of designing nets that can be easily raised and lowered by farmers.
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