monkfish vs saltwater fish

monkfish and saltwater fish both are nouns.

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

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

monkfish: flesh of a large-headed anglerfish of the Atlantic waters of North America
saltwater fish: flesh of fish from the sea used as food

monkfish (noun)	saltwater fish (noun)
fishes having large mouths with a wormlike filament attached for luring prey	flesh of fish from the sea used as food
sharks with broad flat bodies and winglike pectoral fins but that swim the way sharks do
flesh of a large-headed anglerfish of the Atlantic waters of North America