Porcupinefish or Pufferfish or Boxfish?
Both can inflate their bodies by sucking in water but while the pufferfish (left) has a smooth body, the porcupinefish (center) has many small spines all over its body. When the spines are folded flat against the body, they look like little uneven bumps on the body of the porcupinefish.
Boxfishes (aka Trunkfishes) have armored bodies and cannot inflate. They are typically square (bottom right) (cross section), but can also be triangular (top right) or hexagonal, while juveniles are more rounded.