Argentines dont like fish a lot- so most of the good stuff is exported. Not sure why someone would think Argentina doesnt export seafood. It does.
For instance, there is a decent scallop harvest here, but scallops command a global price that makes them too expensive to be saleable in country. We met a guy a couple of years ago who works full time as an international scallop salesman from Argentina, and they harvest, pack, and airship all over the world.
I would imagine its similar with crab, and other more exotic seafood- if the japanese will pay large amounts for fresh, air freighted to Tokyo, and they markets in Argentina cant sell for 1/4 the global price, why even bother trying to sell here?
my experience with farmed salmon is that its tasteless and mealy.
I have a lot of friends who fish King, Copper River, Chinook, Sockeye, and Pink up in Alaska, and having grown up on that, I skip the Chilean farmed stuff.
However, you can get what they call Trucha here, which is a salmon family fish from Patagonia, that is good, natural, and not too expensive.
We have recently discovered Mar Abierto, on Bulnes y Paraguay, which has a lot of quality local seafood, most frozen on the boat, from a company in MDQ. Everything we have had from there has been good, including the Trucha, and unlike say, Ostramar, you cant smell the store from a block away...