PROBLEM TO BE SOLVED: To provide a multi-functional modified type circulation breeding-water for solving the problems of a tiger puffer or tuna thereby to improve the breeding density of those fish species and for simply breeding them in the environment provided.SOLUTION: In a high-density culture of a closed circulation type, actions to lead to the death of bred fish species, such as the mutual bites due to stress, and the collision and abrasion against the tank wall surface of breeding water, are suppressed. By restricting such actions physically by adjusting the clarity and viscosity of the breeding water, the aforementioned actions are physically restricted to improve the breeding density of the bred fish species.【課題】トラフグやマグロなどがもつ諸問題を解決し、これらの魚種の飼育密度を向上させ、かつ簡易的に飼育可能な環境を提供する。【解決手段】閉鎖循環型の高密度養殖において、ストレスによる噛み合いや飼育水槽壁面との衝突やすれといった飼育魚類の斃死に繋がる行動を抑制するため、飼育水の透視度と粘度を調整することにより上記の行動を物理的に制限し、飼育魚類の飼育密度の向上を図る。【選択図】図２
