My fishmonger suggested mako shark as a substitute for tuna. It does not taste all that much like tuna, but responds well to the same cooking techniques and is very tasty. Mako shark fillets about 1 inch thick, 6-8 oz, one per person Old Bay seasoning Kosher salt Vegetable oil Finely minced fresh chives Sweet butter at room temperature For each person being served, mash 1 TB butter and 1 TB chives together, and set aside. Sprinkle the fillets with kosher salt and let sit for about an hour. Rinse off and pat dry with paper towels. Sprinkle both sides with Old Bay, then brush with oil. Heat a heavy skillet over medium-high heat until quite hot - not scorching, as this is not blackened fish! Add the fillets and cook for 2-3 minutes. Flip and continue cooking until almost cooked thru, another 2 minutes or so. Cut a slit in one fillet to check. Transfer to heated plates, top each fillet with a glob of chive butter, and serve.