[en] At present there is a number of requirements imposed on conducting experiments, but also above all on very experimental biological object. It is necessary to fulfil many optimal conditions meeting every aspect of research project, such as the wellfare of the animal associated with appropriate facilities, the shortest time of the experiment with respect to the live organism, reproducibility of examined object, low expenses, results with the greatest applicability to human life, consequently to the environment and many others, well-known as well as being meet daily among scientific community. At least one option is to choose a suitable and inexpensive experimental object, as we have done in our department. Artemia franciscana - invertebrate - is the first and the second more close to eye is Poecilia reticulata -vertebrate. These two species certainly have common water area where they live during their entire life cycle, are very adaptable to the artificial conditions. They also have high reproducibility, which is appropriate for continuation of the experiment. There are interspecies differences as well as particularities within the same species, not least the sensitivity of the organism in the aquatic environment after irradiation, varying duration of experiment. The aim of this work is to show not only the advantages of using these experimental objects, but also their common and different features after irradiation with the same dose of 20 Gy, which is considered as lethal for Poecilia, whereas as one of the low doses for Artemia. (author)