Axis or Registration point

Not sure about the terminology here, but how do I move the axis (or registration point) of an object. For example, I have a fish character and when I rotate the axis is near his nose. Somehow I am responsible for this, but I don’t know how. Is there a way to move that little purple axis mark to the center of the fish so he rotates from the center of his body?

  1. Go to object mode.
  2. Select your object.
  3. Click Editing\Mesh\Center New. This automatically recenters the center of the object to the center of the object. (pfft … what a sentence.)

<edit> BTW this kind of questions go to Blender General. </edit>

Thanks! I appreciate it!