code to play my animation on button press, but it is looping. What do I add to stop this?

I've got a gun in my game to fire, and I've just created the animation for it. I setted up a code so that when I pressed down "fire" (LMB) that the animation would play. How ever it keeps on looping after I pressed it, which obviously is unideal. Here is the code (using Java)

var animation_bool : boolean ;

   function Update()
                  {

       if(animation_bool == true)
                  {
              animation.Play("backfire");

                  }


       if(Input.GetButtonDown("fire"))
                  {
           animation_bool = true;

                 
           }       
                 
          }