The Collaborative International Dictionary of English v.0.48:

Pinfish \Pin"fish`\, n. [So called from their sharp dorsal
   spines.] (Zool.)
   (a) The sailor's choice (Diplodus rhomboides syn. Lagodon
       rhomboides).
   (b) The salt-water bream (Diplodus Holbrooki).
       [1913 Webster]

   Note: Both are excellent food fishes, common on the coast of
         the United States south of Cape Hatteras. The name is
         also applied to other allied species.
         [1913 Webster]

WordNet (r) 3.0 (2006):

pinfish
    n 1: similar to sea bream; small spiny-finned fish found in bays
         along the southeastern coast of the United States [syn:
         pinfish, sailor's-choice, squirrelfish, Lagodon
         rhomboides]