PURPOSE:To obtain a man-made gathering-place for fish for farming fisheries, provided with seawater cleaning function. CONSTITUTION:A hollow part 2 is made at the central part of a block made of cellular concrete formed by blending cement with iron oxide and a blowing base to give a main body 1 of a man-made gathering-place for fish. In seawater 20, structures G and H prepared by inserting iron rods 6 into the hollow parts 2 are arranged at both sides of a structure F made by packing iron particles 3 to the hollow part 2 and a direct electric source 8 is connected to each iron rod of the structures G and H. Iron ion is formed from an anode (+) and ferrous hydroxide is made from a cathode (-). Multiplication of diatoms, plankton, etc., is improved while excellently maintaining adhesion of spores of marine algae by the uneven part of the block made of gas cellular concrete, seawater is cleaned and gathering effect of fishes and shellfishes is bettered.
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