Fish Markets?

I'd hop on the Q or 2/3, get off at Canal Street and walk east. You can get a bag of fresh snow and king crab legs for half the price you'll find over here. I don't mention Sunset Park because depending on which subway you are near, getting there can be a pain in the butt. There are always more trains running faster going into Manhattan than Brooklyn.

There are a couple on Nostrand between St John's & Sterling, but I find the quality is a little hit and miss. Stuff that moves fast in the neighborhood like porgies, whiting, cod, snapper, and the shellfish tend to be fresher and have a pretty decent selection. I'd be a bit more hesitant with other items, but YMMV.

There is one on President at Nostrand and there is one inside Western Beef ( independent of the grocery store). Not bad either... Scrimps, crabs and salmon are good there.

if you want really good fish you should go to the Greenmarket on Grand Army Plaza on Saturdays. I forget the name of the fish stand, but there is only one so you can't miss it. They are friendly, the fish is super fresh and reasonably priced. They are there from March until December (aprox.). Go there early (8-9 am) because their fish goes faaaaaaaaast!

enjoy

Don't know if you want to go over there but in Brownsville you have Slavin and Sons on Rockaway and Belmont. They are pretty famous but the area is pretty rough.

I travel to Slavin and Sons on Belmont off Rockaway. Been going there since my mom use to drag us when we were kids.They service most restaurants and hotels in the city so worth the trek for fresh fish/