I have been looking for an answer lately as well. At some point in the past I either read an article or was told by someone that they are a result of fish being grouped up in tight schools and not because they are fresh fish, but I have not been able to verify that one way or the other recently. Personally I do not feel that it means the fish are fresh as I have landed bass many, many miles up a freshwater river that had so-called sea lice on them.
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