Everything at Barney Greengrass is delectable — the sturgeon, the Nova Scotia salmon, the whitefish — but my favorite is the sable. Black cod with a touch of garlic and paprika, the sable tastes like butter. It’s silky smooth and melts in your mouth. I initially ordered the sable sandwich because I was on the go, but this has become my favorite way to enjoy the fish — sandwiched in a toasted bagel with cream cheese, tomato and onion. A classic, it would seem, but third-generation owner Gary Greengrass warns, “Enjoy it while you can. They’re delicious because they’re wild, but we’re not always going to have this.” Irreversible change such as the extinction of fish is difficult to fathom amid the décor of Barney Greengrass’s old school store and diner, which has remained marvelously unaltered for the past 83 years.