freshwater fish vs pike

freshwater fish and pike both are nouns.

Word	Noun	Adjective	Verb	Adverb
freshwater fish	Yes	No	No	No
pike	Yes	No	No	No

As nouns, pike is a hyponym of freshwater fish; that is, pike is a word with a more specific, narrower meaning than freshwater fish:

freshwater fish (noun)	pike (noun)
flesh of fish from fresh water used as food	any of several elongate long-snouted freshwater game and food fishes widely distributed in cooler parts of the Northern Hemisphere
	medieval weapon consisting of a spearhead attached to a long pole or pikestaff; superseded by the bayonet
	a broad highway designed for high-speed traffic
	a sharp point (as on the end of a spear)
	highly valued northern freshwater fish with lean flesh