BlackSalt Restaurant and Fish Market, Jeff Black's newest venture will open for dinner tomorrow, at 4883 MacArthur Blvd., next door to Addie Bassin's MacArthur Beverages. The phone # is 202-342-9101. Anyone who remembers the late, lamented MacArthur Pharmacy will be amazed at the total transformation of the space. The fish market faces the street, then there is a bar area (full bar and raw bar) and then the dining room and open kitchen, which has a woodgrill and a smoker. The fish market will be opening on Wednesday. Lunch will be added next week. (Full disclosure: I will be working in the fish market.) The menu is quite ambitious, with a selection of small plates, appetizers, several seafood stews, five or six different preparations of mussels, specials and entrees-- almost all will be fish and shellfish. Last week, during a staff training session, Jeff Black explained that because he has four restaurants, the fish and shellfish sold in the fishmarket and served in the restaurant will always be very fresh. Within three or four days, everything will be sold or served, if not at BlackSalt, then at Addie's, Black's Bar and Grill or Black Market, his other places. Jeff is very serious about quality --everything is made from scratch, including stock and fumet, and he insists on top quality ingredients. And he has very demanding expectations of the staff in the interest of customer satisfaction.