Yeah, I just went this morning. I heard about it through this earlier post:
I picked up some crab cakes and a sea bream fillet (which Ian, one of the owners, did in store for me).
The owners were friendly and helpful. They have a website now:
http://www.yongeseafood.ca/ which is still a work in progress.
Besides fish they all have fish-related products, like sauces, breading, shrimp chips, and other groceries.
Address again is 2044 Yonge St.
Check it out!