New Tool Against Dangerous Salmon Parasite
UV treatment has proven to be an effective method for combating the parasite Spironucleus salmonicida in hatchery facilities. This is positive news for stakeholders in the aquaculture industry who have long struggled with this parasite.
Spironucleus salmonicida is a single-celled parasite that can cause disease in farmed salmon at sea. It is believed that the fish are initially infected in freshwater, and the parasite has been notoriously difficult to eradicate in hatchery systems. However, new research shows that proper use of UV light can effectively eliminate this rare but harmful parasite.
Two Types of UV Technology Tested
Researchers tested two different UV lamp types in a controlled laboratory trial: low-pressure and medium-pressure lamps. The parasite was exposed to various UV doses, and survival after treatment was examined. The results showed that medium-pressure lamps were significantly more effective than low-pressure lamps, even at lower doses.
“With medium-pressure lamps, we observed no surviving parasites at a dose of 50 mJ/cm² or higher,” says research manager Lill-Heidi Johansen at Nofima.
Even at lower doses of 10 and 25 mJ/cm², the parasites were so weakened that they died within 48 hours.
A Clear Recommendation
Based on the findings, researchers recommend a dose of at least 50 mJ/cm² when using medium-pressure UV lamps in hatchery facilities.
“However, the dose should be adjusted according to water quality. For example, a higher level of organic material in the water can reduce the effectiveness of UV treatment,” Johansen points out.
Important for the Industry
The findings are significant for the aquaculture industry. Effective control of Spironucleus salmonicida can result in healthier fish and improved production.
“This provides us with a new tool in the fight against this troublesome parasite,” Johansen says.
The Way Forward
Researchers will now begin fish trials involving an infection with the Spironucleus salmonicida parasite in RAS (Recirculating Aquaculture System) facilities at the Fish Health Laboratory at the Aquaculture Station in Tromsø. In the trial, the UV dose (50 mJ/cm²) found effective in initial tests will be further evaluated. Researchers will also study the effects of ozone treatment.
The study will also investigate where in the RAS system the parasite is located. Senior researcher Carlo Lazado, who is responsible for the upcoming trial, looks forward to the next steps.
“It is extremely important to understand where the parasite is located in the RAS system to develop the best possible disinfection strategies in the future,” he concludes.
Fact Box: UV Dose
UV lamps that emit ultraviolet light disinfect water. This disrupts the genetic material of harmful microorganisms in the water. Light intensity is measured in millijoules per square centimetre (mJ/cm²). Higher doses are required for more resistant organisms.
In the trial, researchers used two UV lamp types: low-pressure and medium-pressure. Different doses were tested to determine the level required to achieve a 99.9% reduction of the parasite Spironucleus salmonicida.
Researchers found that even low UV doses (10-25 mJ/cm²) using medium-pressure lamps were sufficient to weaken the parasites to the point that they died within 48 hours. This is promising news, as it means less energy can be used while still achieving effective results.
The research project is funded by FHF and led by the Institute of Marine Research.
(FHF Project No. 901831: Spironucleus salmonicida Infections and Spironucleus in Norwegian Aquaculture: Transmission Routes, Host Spectrum, and Prevention (SpiroFri))
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