A few years ago I went to this market and found it just okay. I am pleased to report that it seems to have much improved.
They seem to specialize in whole fish and usually have about 10 varieties available. Recently they had black bass, white bass, striped bass, tilapia, rock cod, red snapper and perch and probably a few others. The fish are laid out on ice so that you can smell, poke and examine which I like to do when buying fish.
The prices are very excellent, the whole fish I mentioned above were between $1.50 and $3.50 per pound.
They also sell live crab, lobster, tilapia, and carp. I have had the Dungeness crab ($2.29/lb recently) and been very happy with it.
In addition, they sell shellfish, fillets, and steaks (of fish). I have not tried these.
Mission Near 23rd.
Do not confuse with the Wang Fat which is 5 blocks away and dirty, smelly, and a home to a large fly population.