sea bass vs saltwater fish

sea bass and saltwater fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea bass	Yes	No	No	No
saltwater fish	Yes	No	No	No

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

sea bass (noun)	saltwater fish (noun)
any of various food and sport fishes of the Atlantic coast of the United States having an elongated body and long spiny dorsal fin	flesh of fish from the sea used as food
the lean flesh of a saltwater fish of the family Serranidae