Well, you can rotate about the line through the centers of both the top and bottom triangles through an angle of radians multiple times. 3 times gets you back to your starting point. You can also flip the prism (interchange top and bottom) followed by a rotation through radians about the axis through the centers of the top and bottom. Finally, you can rotate about an axis going through one lengthwise edge, the center of the prism, and the center of the opposite face. That rotation would be through radians.

Those are all the symmetries I can think of.