Provided are a closed rearing method and a closed rearing apparatus which can decompose and remove ammonia contained in rearing water without supplying an excessive amount of ozone and can also suppress generation of toxic oxidants. In a closed rearing method for aquatic organisms and marine animals involving an ozone treatment for decomposing ammonia in rearing water by supplying a gas containing ozone into the rearing water, the closed rearing method is characterized in that aquaculture is performed in a closed environment by a first step for determining the ozone concentration of the gas and pH conditions of the rearing water suitable for reducing the amount of generation of toxic oxidants by previously treating the rearing water to reduce ammonia contained therein to the target value by using an apparatus for actually conducting the treatment and a second step for conducting an ozone treatment of the rearing water according to the suitable ozone concentration and pH conditions determined in the first step.
