PURPOSE: To enable fish culture to be done in the open sea with strong wave, free from rocking and/or twisting of the titled net due to the wave, by charging or discharging the central (non)metallic supporting pipe with water to effect sinking and floating the net.

CONSTITUTION: In a fish preserve net frame composed of the central (non)metallic supporting pipe 1, arms 2, 4 radially extending from this pipe and outer frames 5, 3, 7, water is charged through a hose 9 into the pipe 1 or discharged through an outlet 10 from the pipe 1 to increase or decrease the amount of water in the pipe 1, respectively, to perform sinking and floating of the above frame as desired, thus enabling fish culture to be done in the open sea with strong wave.