The Collaborative International Dictionary of English v.0.48:

balloonfish \bal*loon"fish`\, balloon fish \bal*loon" fish`\
   (Zool.)
   A fish of the genus Diodon (such as Diodon holocanthus)
   or the genus Tetraodon, having the power of distending its
   body by taking air or water into its dilatable esophagus. It
   is similar to but smaller than the porcupinefish. See
   Globefish, and Bur fish.
   [1913 Webster + WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Bur fish \Bur" fish`\ (Zool.)
   A spinose, plectognath fish of the Allantic coast of the
   United States (esp. Chilo mycterus geometricus) having the
   power of distending its body with water or air, so as to
   resemble a chestnut bur; -- called also ball fish, balloon
   fish, and swellfish.
   [1913 Webster]