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]