poeciliid fish vs platy

poeciliid fish and platy both are nouns.

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

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

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

Other hyponyms of poeciliid fish include Gambusia affinis, mosquitofish, Platypoecilus maculatus, mollie, molly.

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