mosquitofish vs poeciliid fish

mosquitofish and poeciliid fish both are nouns.

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

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

mosquitofish: silvery topminnow with rows of black spots of tropical North America and West Indies; important in mosquito control
poeciliid fish: small usually brightly-colored viviparous surface-feeding fishes of fresh or brackish warm waters; often used in mosquito control

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

mosquitofish (noun)	poeciliid fish (noun)
silvery topminnow with rows of black spots of tropical North America and West Indies; important in mosquito control	small usually brightly-colored viviparous surface-feeding fishes of fresh or brackish warm waters; often used in mosquito control