mahimahi vs saltwater fish

mahimahi and saltwater fish both are nouns.

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

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

mahimahi: the lean flesh of a saltwater fish found in warm waters (especially in Hawaii)
saltwater fish: flesh of fish from the sea used as food

mahimahi (noun)	saltwater fish (noun)
large slender food and game fish widely distributed in warm seas (especially around Hawaii)	flesh of fish from the sea used as food
the lean flesh of a saltwater fish found in warm waters (especially in Hawaii)