brook fish

from The Collaborative International Dictionary of English v.0.48

Killifish \Kil"li*fish`\, n. (Zool.)
   Any one of several small American cyprinodont fishes of the
   genus {Fundulus} and allied genera. They live equally well in
   fresh and brackish water, or even in the sea. They are
   usually striped or barred with black. Called also {minnow},
   and {brook fish}. See {Minnow}.
   [1913 Webster]