scup vs saltwater fish

scup and saltwater fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
scup	Yes	No	No	No
saltwater fish	Yes	No	No	No

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

scup: lean flesh of fish found in warm waters of southern Atlantic coast of the United States
saltwater fish: flesh of fish from the sea used as food

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

scup: flesh of fish found in colder waters of northern Atlantic coast of the United States
saltwater fish: flesh of fish from the sea used as food

scup (noun)	saltwater fish (noun)
porgy of southern Atlantic coastal waters of North America	flesh of fish from the sea used as food
found in Atlantic coastal waters of North America from South Carolina to Maine; esteemed as a panfish
lean flesh of fish found in warm waters of southern Atlantic coast of the United States
flesh of fish found in colder waters of northern Atlantic coast of the United States