The Collaborative International Dictionary of English v.0.48:

Spawner \Spawn"er\, n.
   1. (Zool.) A mature female fish.
      [1913 Webster]

            The barbel, for the preservation or their seed, both
            the spawner and the milter, cover their spawn with
            sand.                                 --Walton.
      [1913 Webster]

   2. Whatever produces spawn of any kind.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spawner
    n 1: a female fish at spawning time