Fish sandwiches are a lunchtime staple, whether Haddock in Boothbay Harbor, ME; Salmon in Seattle, WA; Flying fish in Bridgetown, Barbados; Mahi in Key Largo, FL; Walleye in Ely, MN; Catfish in New Orleans, LA; or Cod at any pub, anywhere. While all are delicious, a grouper sandwich in St. Petersburg, FL is unsurpassed. Groupers come in several varieties, Black, Red, Yellowedge and Gag being the more popular ones, at least based on what one can find at a local St. Petersburg, FL fish market. Black are the most expensive, but with Black and Gag looking only subtly different, and with Gag landings exceeding Black, my guess is that these may be interchanged, but who knows. If the piece of fish looks thick and cooks up nice and flakey, then it is probably grouper. If it looks thin and at a bargain price, it is likely fish mystere, as unfortunately occurs all too often.