I' ve long bought lobsters at pretty good prices in CTown but tended to avoid the finfish. Just rarely found the quality to be there.
Lately I've been picking up some fish at Jia Ho, the old CMart on Washington, Happy Family and the store underneath Winsor Cafe.
Bought several mackeral, lobsters, sea clams, squid and more. These places have all upped their game. With fish, stick to whole fish, bright clear eyes, red gills.
Where else can you have the experience of a live eel slither over your feet while you're shopping?..:)