The Collaborative International Dictionary of English v.0.48:

Redfin \Red"fin`\ (-f?n`), n. (Zool.)
   A small North American dace (Minnilus cornutus, or
   Notropis megalops). The male, in the breeding season, has
   bright red fins. Called also red dace, and shiner.
   Applied also to Notropis ardens, of the Mississippi valley.
   [1913 Webster]