When I was learning to cook, few Americans knew from grilled fish. Today, I don’t have to convince you of its virtues. You are probably comfortable grilling tuna steaks or salmon fillets. But there comes a time when a griller wants to perform feats of fiery derring-do to impress a crowd. That’s why every serious barbecue buff should know how to barbecue a whole salmon. Just don’t let on that this is one of the easiest fish dishes in the world to cook.