I just went to this new fishmonger called Hooked Inc @ 888 Queen St E (416-828-1861) and was very impressed. They are focusing on sustainable seafood with very knowledgable people manning the counters.
They have board listing the seafood they are selling. I ended up buying some Halibut, line-caught, from the Bering Sea and it was absolutely delicious. The fishmongers that focus on sustainable seafood and that actually post where the seafood came from and how it was caught are few and far between, if any, in Toronto.
I'll be making this a regular place to purchase my seafood.
The website is http://www.hookedinc.ca/