Synonyms for Topminnow (same or very similar meaning)
WordNet sense 1 (small usually brightly-colored viviparous surface-feeding fishes of fresh or brackish warm waters; often used in mosquito control):
live-bearer, poeciliid, poeciliid fishWordNet sense 2 (freshwater fish of Central America having a long swordlike tail; popular aquarium fish):
helleri, swordtail, Xyphophorus helleriFrom the ODE community, based on WordNetadd/edit