molly vs poeciliid fish

molly and poeciliid fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
molly	Yes	No	No	No
poeciliid fish	Yes	No	No	No

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

molly: popular aquarium fish
poeciliid fish: small usually brightly-colored viviparous surface-feeding fishes of fresh or brackish warm waters; often used in mosquito control

Other hypernyms of molly include live-bearer, poeciliid, topminnow.

molly (noun)	poeciliid fish (noun)
popular aquarium fish	small usually brightly-colored viviparous surface-feeding fishes of fresh or brackish warm waters; often used in mosquito control