sea bream vs saltwater fish

sea bream and saltwater fish both are nouns.

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

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

sea bream: flesh of any of various saltwater fishes of the family Sparidae or the family Bramidae
saltwater fish: flesh of fish from the sea used as food

sea bream (noun)	saltwater fish (noun)
any of numerous marine percoid fishes especially (but not exclusively) of the family Sparidae	flesh of fish from the sea used as food
flesh of any of various saltwater fishes of the family Sparidae or the family Bramidae