weakfish vs saltwater fish

weakfish and saltwater fish both are nouns.

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

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

weakfish: lean flesh of food and game fishes of the Atlantic coast of the United States
saltwater fish: flesh of fish from the sea used as food

weakfish (noun)	saltwater fish (noun)
food and game fish of North American coastal waters with a mouth from which hooks easily tear out	flesh of fish from the sea used as food
lean flesh of food and game fishes of the Atlantic coast of the United States