The Collaborative International Dictionary of English v.0.48:

Grindle \Grin"dle\, n. (Zool.)
   The bowfin; -- called also Johnny Grindle. [Local, U. S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

grindle
    n 1: primitive long-bodied carnivorous freshwater fish with a
         very long dorsal fin; found in sluggish waters of North
         America [syn: bowfin, grindle, dogfish, Amia calva]