whalesucker vs sucking fish

whalesucker and sucking fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
whalesucker	Yes	No	No	No
sucking fish	Yes	No	No	No

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

whalesucker: large blue Pacific remora that attaches to whales and dolphins
sucking fish: marine fishes with a flattened elongated body and a sucking disk on the head for attaching to large fish or moving objects

Other hypernyms of whalesucker include remora, suckerfish.

whalesucker (noun)	sucking fish (noun)
large blue Pacific remora that attaches to whales and dolphins	marine fishes with a flattened elongated body and a sucking disk on the head for attaching to large fish or moving objects