A piece of 3-cm thick polyethylene raft covered almost entire water surface except a 15 cm × 15 cm corner cut open, allowing an automatic feeder release pellet feed into the water. A cut plant stem 25.1 ± 3.7 cm or 7.8 ± 0.5 g was wrapped around with layers of sponge, stuffed in a black plastic ring (4.5-cm D) then fit into one of the 63 evenly distributed round holes.