Jumping salmon: A cure for sea lice?
A study published in last week’s Journal of Animal Science may allow salmon farmers to more effectively treat sea lice and re-collect the treatment chemicals after their use.
In the 1990s, attempts were made to get farmed salmon to remove sea lice themselves when they jumped by adding a thin layer of oil containing the treatment chemical pyrethrum on the surface. As salmon jumped through the surface, the oily treatment made contact with the sea lice and killed them. Early trials of this method were promising, however full-scale cage trials proved ineffective as the salmon did not jump frequently enough and the treatment chemical broke down in sunlight.
To enhance the effectiveness of this method, in 2010 the researchers tested whether the natural jumping behavior of salmon could be increased and directed. They removed the ability of groups of salmon to access the surface for different periods with a shallow cage roof and recorded their jumping after the surface became accessible again. Surface removal for one to two days induced 93 percent of salmon to jump in the two hours after surface access was re-instated. Salmon without surface access for one to two days jumped on average two to three times per fish.
The results indicated that removal of surface access for short periods leads to loss of air from the swim bladder and cause slight negative buoyancy. This creates a behavioral driver for salmon to jump, swallow air and fill their swim bladders once surface access is re-instated.
“Now that a technique exists that means salmon jump frequently and predictably, the door is open for the development of new sea lice treatments that can be infused in oil,” said Frode Oppedal of the Institute of Marine Research.
The study was conducted by researchers from the Centre for Research-Based Innovation in Aquaculture Technology at SINTEF Fisheries and Aquaculture, the University of Melbourne in Australia, and the Fish Welfare Group of the Institute of Marine Research.