Of course in the more juvenile crowd, saying, "I think I'll have some tuna" it will probably be assumed your going downtown on your girlfriend. So around frat houses it might be worth avoiding having to walk down a row of hi-5's to specify that you are indeed talking about the fish.
In all other scenario's tuna will do. Unless you're part of the Dolphins organization, in which case they might think your talking about Bill Parcells. But I don't have a habit of saying, "I'm going to eat a ham-pig sandwich". So I suppose dropping the 'fish' from a 'tuna-fish' sandwich would be accurate.