Ecological Systems and Devices Annotation << Back Development of Daphnia and Saprotrophic bacteria in Stationary Conditions and in the Presence of Hydrogen Peroxide in the Culture Medium Dallakyan G.A., Gershkovich D.M., Akulova A.Yu., Ilyinsky V.V. In stationary conditions, when there are no daphnia in the environment, daphnia develop naturally with oxygen consumption. When hydrogen peroxide is added to the environment at a concentration of 10–4 M, daphnia consume very little oxygen compared to the control. That is, this concentration is partially toxic. At a hydrogen peroxide concentration of 3.10–4 M, the oxygen concentration in the medium increases during the fi rst 6 days of culture growth, which is associated with the decomposition of hydrogen peroxide, i.e., the control sample and the experimental sample show the rate of decomposition of hydrogen peroxide, oxygen consumption by daphnia was not detected. This concentration is toxic to daphnia. At concentrations of hydrogen peroxide in the environment of 10–3 M, all daphnia die, the oxygen content refl ects the kinetics of hydrogen peroxide decay. It is important to note that, in the presence of daphnia, the These results show that when daphnia die, they release substances into the environment that catalyze the decomposition of hydrogen peroxide at a higher rate. It has been shown that in the presence of daphnia, the restoration of the number of bacteria after exposure to hydrogen peroxide occurs faster than in a pure cultivation medium without living organisms. decay of hydrogen peroxide occurs more intensively than when they are not in the environment. That is, in the process of their life activity, crustaceans create a favorable environment for the development of bacteria, thus, in stationary conditions and low concentrations of hydrogen peroxide, daphnia consumes oxygen. At high concentrations of hydrogen peroxide, daphnia die and mineral substances are released into the environment. As a result, these substances catalyze the decomposition of hydrogen peroxide. It has been shown that, in the presence of daphnia in the environment, the number of bacteria is greater than when they are not present. In our work, no reliable direct connection was found between the content of bacteria and the decomposition of hydrogen peroxide in low concentrations. This interaction occurs indirectly through daphnia. Keywords: Hydrogen peroxide, daphnia, saprophytic bacteria. DOI: 10.25791/esip.7.2025.1536 Pp. 39-50.