The Collaborative International Dictionary of English v.0.48:

Mojarra \Mo*jar"ra\, n. [Sp.]
   Any of certain basslike marine fishes (mostly of tropical
   seas, and having a deep, compressed body, protracile mouth,
   and large silvery scales) constituting the family Gerridae,
   as Gerres plumieri, found from Florida to Brazil and used
   as food. Also, any of numerous other fishes of similar
   appearance but belonging to other families.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Cow-pilot \Cow"-pi`lot\ (kou"p[imac]`l[u^]t), n. (Zool.)
   A handsomely banded, coral-reef fish, of Florida and the West
   Indies (Pomacentrus saxatilis); -- called also mojarra.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mojarra
    n 1: small silvery schooling fishes with protrusible mouths
         found in warm coastal waters