A grey fat fish with black fins,
      black spots, black mask. View of its tail.

On a background of corals
      a grey puffer fish with black fins, black spots, black mask, hard
      beak.
Arothron bites fire coral

Puffer's tail

( Arothron diadematus )

When an arothron swims, unlike fast fish it doesn't wave its body. It also doesn't use its tail. Sometimes arothron curves its tail like at this photo, then it swims using only pectoral fins.