That wouldn't even work. You have to grow salmon in freshwater to a certain size before you can grow them in the sea, it's done in tanks on land here in Norway

That wouldn't even work. You have to grow salmon in freshwater to a certain size before you can grow them in the sea, it's done in tanks on land here in Norway (the fishery directorate would certainly not let them use rivers). I worked at the University library when I studied, I remember there was a ton of outdated books from the early development of salmon aquaculture. Salmon farming didn't even succeed until the late 60s, it took a lot longer to make it profitable. They tried a lot of wild stuff, some of it was ecologically questionable to put it mildly (like "havbeite", the idea of forgoing enclosures entirely and just release the smolt to sea, hoping to catch it later). But regulation has caught up to the industry somewhat. Of course, now the Norwegian owned industry does a lot of the bad stuff it's no longer allowed to do in Norway in Chile instead.