I think they are interchangeable. I suppose I use water heater but if one were to use hot water heater, clearly the intent is known. I mean why do they call it toilet paper when the the toilet is just where it ends up. And it doesn't really resemble paper that I'm familiar with. See what I'm saying?
Tuna is a fish. Dolphins are mammals. There is also a dolphin fish that is called Mahi Mahi when served at restaurants. Probably because people think the mammal dolphins are cute and are squeamish about eating them. Unless they're Japanese who eat just about anything. I don't know if it's correct but for me if it comes in a can it's tuna fish. If it's grilled then it's just tuna.
I don't say the fish part. I suppose it's like saying hamburger meat. It's not ham (it could be I suppose) but clearly a hamburger is meat. It's not a veggie or a fruit or a grain. I ask my son a lot, exactly what part of the chicken is a finger, a nugget, a tender? Why do New Yorkers call it a pizza "pie"?
If I eat a hamburger I call it a hamburger but it's made from hamburger meat. Not all ground meat is for hamburger. .ie, If you want to grill some hamburger pick up some hamburger meat at the store.
