freshwater fish vs seafood

freshwater fish and seafood both are nouns.

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

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

freshwater fish: flesh of fish from fresh water used as food
seafood: edible fish (broadly including freshwater fish) or shellfish or roe etc

freshwater fish (noun)	seafood (noun)
flesh of fish from fresh water used as food	edible fish (broadly including freshwater fish) or shellfish or roe etc