Spiny Puffer - Length: 20 inches
Porcupinefish - Length: 3 feet
The Spiny Puffer, also known as Barred Spiny Puffer, Balloonfish, is very similar to the Porcupinefish but you can tell the difference by the large black blotches on its back. The picture shows the Spiny Puffer relaxed with its spines down, while the Porcupinefish is shown puffed up. Instead of the large black blotches of the Spiny Puffer the Porcupinefish has many smaller spots.
They puff up by pumping water into their stomachs. Then the stomach inflates and the spine arches to accomodate the organ's expansion. Pockets of the stomach soon get shoved above and around the spine, making the fish nearly spherical.