carp vs freshwater fish

carp and freshwater fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
carp	Yes	No	Yes	No
freshwater fish	Yes	No	No	No

As nouns, freshwater fish is a hypernym of carp; that is, freshwater fish is a word with a broader meaning than carp:

carp: the lean flesh of a fish that is often farmed; can be baked or braised
freshwater fish: flesh of fish from fresh water used as food

carp (noun)	freshwater fish (noun)
any of various freshwater fish of the family Cyprinidae	flesh of fish from fresh water used as food
the lean flesh of a fish that is often farmed; can be baked or braised

carp (verb)	freshwater fish (verb)
raise trivial objections