WordNet (r) 3.0 (2006):

topminnow
    n 1: small usually brightly-colored viviparous surface-feeding
         fishes of fresh or brackish warm waters; often used in
         mosquito control [syn: topminnow, poeciliid fish,
         poeciliid, live-bearer]
    2: freshwater fish of Central America having a long swordlike
       tail; popular aquarium fish [syn: swordtail, helleri,
       topminnow, Xyphophorus helleri]