The purpose of the present invention is to provide a circulating fish culture method and a circulating fish culture device, whereby a treatment for removing ammonia that is harmful to fish can be conducted while preventing the generation of toxic oxidants caused by an excessive treatment, and the ammonia removal treatment can be conducted depending on the increase or decrease of the amount of ammonia discharged from the fish to thereby prevent the accumulation of ammonia in culture water. To achieve this purpose, provided is a method for treating culture water in a circulating fish culture tank, in which aquatic organisms are fed, using a fish culture device main body, wherein a means comprising the following steps is employed: a first step for, in preliminarily treating the culture water with ozone or hypochlorous acid, determining the decomposition speed of ammonia and setting a target remaining amount of ammonia after a decomposition treatment a second step for determining the amount of ammonia in the culture water and calculating the treatment time required for the reduction to the target remaining amount of ammonia on the basis of the decomposition speed of ammonia a third step for treating the culture water with ozone or hypochlorous acid for a period of time calculated in the second step and thus decomposing ammonia in the culture water and a fourth step for returning the culture water that has been subjected to the decomposition treatment in the third step to the fish culture tank.Le but de la présente invention est de fournir un procédé destiné à faire circuler un élevage de poissons et un dispositif destiné à faire circuler un élevage de poissons, moyennant quoi un traitement permettant déliminer lammoniac qui est nocif pour les poissons peut être réalisé tout en empêchant de générer des oxydants toxiques provoqués par un traitement excessif, et le traitement délimination de lammoniac peut être réalisé en fonction de laugmentation ou de la diminution de la
