People often say “tuna fish” when they’re talking about tuna. It seems to be chiefly used when referring to the food, and not to the actual living fish. Furthermore it seems only to apply to canned, shredded tuna; you never hear a person (or a menu) speak of tuna fish sushi, seared tuna fish steak, or anything like that. “Tuna” can be high-class fare, but “tuna fish” is the domain of cheap sandwiches alone.
No other fish has this redundant name. Nobody talks about salmon fish, or trout fish, or anything like that. Every now and then you will see “codfish” used, but even that is fairly rare and seems to only be used in conjunction with oil, extract or other products made from the cod - never a food.
This stuff doesn’t really count because if the word “fish” weren’t there, the word would have a completely different meaning. The equivalent to what I’m talking about would be to say “sunfish fish” or somesuch.
ETA: a bar here has, on the menu, a “CATFISH FISH SANDWICH”.
It seems to me that I hear “tuna fish” a lot less often than I used to. It has kind of an old-fashioned ring to me.
Googling turns up many more instances of “tuna sandwich” than “tuna fish sandwich.” Similarly, “tuna salad” vs. “tuna fish salad.”
On an only slightly related note, the breed commonly known as German Shepherd is called German Shepherd Dog by the American Kennel Club and other registries. In this case, it’s a direct translation from the German.
