New sensitivity test for sea lice larvae developed.
MSD Animal Health has announced the development of the first sensitivity test for sea lice larvae, providing a new tool to monitor resistance in aquaculture.
Until now, sensitivity testing with emamectin benzoate (EMB) has only been conducted on adult and pre-adult sea lice. However, MSD and Veso have now demonstrated that such testing is also possible for larvae, the company said in a statement on Monday.
“This gives us an entirely new monitoring tool to track resistance development in sea lice larvae,” said veterinarian Lene Høgset of MSD Animal Health. “This has significant practical implications for us, fish farmers, and fish health professionals.”
EMB is the most widely used active ingredient in medicated feed treatments for sea lice in Norway. The company believes the test could serve as an important documentation tool for fish health professionals prescribing feed-based sea lice treatments, as it would help meet the regulatory requirement for “relevant sensitivity testing” under Section 9 of Norway’s sea lice regulations.
Fish farmers have long observed that when using feed-based treatments with EMB, sea lice larvae fail to attach to salmon. Now, this effect has been scientifically confirmed for the first time in a laboratory setting.
“The new test showed that EMB immobilised larvae that were resistant to the treatment. This can serve as a tool to predict the degree of preventive effect that emamectin has,” MSD said.
Sigmund Sevatdal of Veso, who played a key role in developing the sensitivity test, was engaged by MSD Animal Health, which produces the most widely used feed-based sea lice treatment.
“We conducted bioassays in the autumn, testing various concentrations of EMB and examining the effects on sea lice larvae. The results are clear—EMB is effective against copepodite-stage larvae even at low concentrations, which explains its preventive effect,” said Sevatdal.
