The Collaborative International Dictionary of English v.0.48:

dollarfish \dollarfish\ n.
   1. small food fish (Poronotus triacanthus) of the Atlantic
      coast.

   Syn: Poronotus triacanthus.
        [WordNet 1.5]

   2. any of several silvery marine fishes with very flat
      bodies.

   Syn: moonfish, Atlantic moonfish, horsefish, horsehead,
        Selene setapinnis.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dollarfish
    n 1: small food fish of Atlantic coast [syn: dollarfish,
         Poronotus triacanthus]
    2: any of several silvery marine fishes with very flat bodies
       [syn: moonfish, Atlantic moonfish, horsefish,
       horsehead, horse-head, dollarfish, Selene setapinnis]