In the course of studying the biomechanical characteristics of hydrobionts there appears a need to apply the theory of similarity of living objects. Along with the theory of similarity, the theory of dimensions is observed. There is considered the multiphysical similarity of hydrobionts of the same species, based on the theory of physical similarity of A. A. Nedostup. One of the tasks of studying the mechanics and hydrodynamics of living systems (hydrobionts) in the aquatic environment is to automate the collection of statistics with subsequent visualization of the characteristics of hydrobionts using augmented reality technologies. Based on the similarity theory, the rules of physical similarity have been developed, similarity criteria have been obtained with respect to geometric, mechanical, hydroacoustic, hydrodynamic, thermodynamic, and optical characteristics of hydrobionts. An important component of similarity is to preserve the physical nature of the original phenomena in the model. Based on the scale of the multiphysical similarity of hydrobionts, the criteria for the similarity of hydrobionts are determined. There is considered the solution of the problems of describing the biomechanics of hydrobionts in recirculation aquaculture systems, where only one species of hydrobionts is grown at the same time. The importance of studies of biomechanics of aquatic organisms in certain habitat conditions, in our case in an artificial enclosed space, with artificial lighting, feeding, cleaning system, etc., is explained by the need to increase fish productivity and environmental friendliness of fish farming, which requires automation of the growing process. Automation tasks require a preliminary mathematical description of processes in order to build simulation models. In turn, for a mathematical description of the growth process of a growing object, it is necessary to derive mathematical dependencies linking the target characteristics of the hydrobionts with the initial data of breeding conditions and a set of characterizing parameters of the object itself, including behavioral ones.