The device consists of five parts: a steel framed buoyan body equipped' with platic floats; a cylindrical polyethylene coated with density plastic woven cloth enclosure bag, 5.7 m in height, 6 m in girth, 2.86 m² in area and 14.3 m³ in capacits; a steel framed, plastic woven cloth covered basal plate which is the bottom of the enclosure; an inner net inside the enclosure bag nclosure; an inner net inside the enclosure bag, used to catch / examine experimental fish, and a 90 W mothor operated water. stirre fixed at the center of the bag mouth, used to stin the water in the bag periodically to keep the water mixing inside the bag equal to that outside it.

To fill the enclosure a “sinking and rising" method is used. In this method first the enclosure is made depressed so as to keep the buoyant body (with no floats at the time) resting directly on the basal plate and sunk to the 5m depth; then the buoyant body is pulled up out of the water surface with the basal plate left unmoved by its weight, so that the enclosure is filled with a water column equal to that outside it. The enclosure is equipped with floats and anchored on the chosen site at last.

The water stirrer operated for 50 min at 10:00 a.m. and 15:00 p.m. whenever the weather is calm or nearly calm. Observations showed that this was enough to keep water mixing inside the enclosure equal to that outside it.

The maximum light shading rate of the enclosure was about 26.7% at the beginning and 33.3% in the end. The chief problem was the periphyton (especially epiphyton) which propagate on the inner surface of the enclosures, interfering with the illumination and water quality of the enclosures. The authors suggest manuallybrushing it off periodically or stocking certain fish which feed on periphyton in them as measures to solve it.