The system foresees for each plate (1) an autonomous mechanical structure composed of one section bar (3) connected to a gripper that holds a plate (1) as well as of another section bar (10) and at least two support arms (5, 5′, 6, 6′) hinged upon said section bars (3, 10); the structure is fixed to a section bar (9) that is in turn fixed to the display counter or window near the base of the tank; the support arms (5, 5′, 6, 6′) differ in length; two supports (4, 4′, 11, 11′) are fixed to each section bar (3, 10); said supports constitute the hinge members upon which the ends of the support arms (5, 5′, 6, 6′) fit; each plate (1) can both move in a parallelogram motion with translation parallel to the display counter or window, and open like a casement window using the pin (7) of the shorter support arm (5, 5′) as a pivot; the system also contains a spring closing mechanism and a lock (18).