On Slice, again, that's a better question for an official from Health Canada and the Veterinary Drugs Directorate. It is my understanding of the pharmacokinetics of Slice that it is distributed very well inside the fish. It takes some time, once it goes in the mouth, to accumulate in the mucus and the skin. And then the lice get exposed to it and it kills the lice. But it doesn't last very long in the fish.
On April 14th, 2010. See this statement in context.