The Collaborative International Dictionary of English v.0.48:

live-bearer \live-bearer\ n.
   Any fish of the family Poeciliiidae, small usually
   brightly-colored viviparous surface-feeding fishes of fresh
   or brackish warm waters, often used in mosquito control.

   Syn: topminnow, poeciliid fish, poeciliid.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

live-bearer
    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]