That's a very good question. Thank you.
The Canadian Food Inspection Agency will do random spot-testing of declared aquaculture products—the things that are farmed and being imported into Canada—to ensure that there are not banned veterinary drug residues or other therapeutants often used by unscrupulous producers to clean up fungal infections and other potential pathogens in their farm-raised seafood.
If, for example, I am an exporter in another country who has dirty fish and I mislabel it as “wild”, I get more money for it and circumvent the screening process for these kinds of banned veterinary drugs. The assumption is that it's wild, so it shouldn't have been treated in this manner.