The Collaborative International Dictionary of English v.0.48:

Loach \Loach\ (l[=o]ch), n. [OE. loche, F. loche.] (Zool.)
   Any one of several small, fresh-water, cyprinoid fishes of
   the genera Cobitis, Nemachilus, and allied genera, having
   six or more barbules around the mouth. They are found in
   Europe and Asia. The common European species (Nemachilus
   barbatulus) is used as a food fish.
   [1913 Webster]

WordNet (r) 3.0 (2006):

loach
    n 1: slender freshwater fishes of Eurasia and Africa resembling
         catfishes