why not say steak cow? or brocoli vegetable, maybe bread wheat...
pleonasm
plē′ə-năz″əm
noun
The use of more words than are required to express an idea; redundancy.
An instance of pleonasm.
A superfluous word or phrase.
It is more like saying Kobe beef. Tuna is a type of fish, so it not quite redundant. It just seems that way because most people know tuna is a fish. I hear it used a lot, so was just curious if it was a thing in some regions or not
not really
kobe beef is raised in Japan's Hyōgo Prefecture according to rules set out by the Kobe Beef Marketing and Distribution Promotion Association. its quite literally its full name created by a company
tuna is a fish not a marketing campaign, therefore, saying tuna fish is a pleonasm