There is more to tuna than the mayo-based sandwich filler. In fact, if there is one fish that can handle a robust marinade and the fire of the grill, it would be tuna. Tuna is thick and dense, and it holds its shape while you take the time to sear it golden brown. The key is choosing which kind of tuna is best to use. There are a number of types of tuna available, from albacore and skipjack (which are popular candidates for canning) to meatier bluefin tuna and ahi (also known as yellowfin), which are excellent fish choices for grilling. Bluefin, with its dark, meaty color and flavor, is the king of tuna—and the priciest. Ahi is the next best option and my favorite. It’s slightly less expensive, milder in flavor, and paler in color than bluefin, with a deep rose hue that browns with cooking. This is the …