Farmers worldwide consider sea lice the biggest threat to their industry and say the persistent problem is making the fish more expensive to consumers.
But around 2009, the lice appeared to become resistant to the pesticide, and they have spread globally since.
The industry's key mistake was reacting when the lice evolved to survive pesticide, Carr said, rather than “getting ahead in the game.” “The efficacy went away and pressure developed to create new treatments,” said Kris Nicholls, chief operating officer at Cooke, a major player in world salmon farming.
The lice can grow to about the size of a pea and lay thousands of eggs in their brief lifetime.
But Atlantic salmon have held their own with sea lice in the wild for centuries, and fish farmers managed them in aquaculture environments for many years.
And the company uses a pair of boats capable of pumping 10,000 fish at a time into a hydrogen peroxide bath, which kills most of the lice, although it also can stress and kill some fish.