The analysis of kinetic curve of redox potential changes (ORP) of aqueous medium in the process of loach embryo population development at 17°C was conducted. The system of critical points defining periodization of the major stages of embryo development was identified on the ORP curve in the time interval up to τ(0) using novel methods for processing of nonlinear signals. It was shown that τ(0) was a natural periodization parameter of main morphological changes in an embryo known in the developmental biology.