A.B. Burlakov – Dr. Sc. (Biol.), Professor, Leading Research Scientist, Department of Ichthyology, 

Faculty of Biology, Lomonosov Moscow State University E-mail: burlakovao@mail.ru

A.F. Gadzaov – Ph.D. (Eng.), Associate Professor, Department of Applied Mathematics, Moscow Technological University E-mail: gadzaov_alex@yandex.ru

A.S. Machikhin – Ph.D. (Phys.-Math.), Leading Research Scientist, Scientific and Technological 

Center of Unique Instrumentation of RAS Е-mail: machikhin@ntcup.ru

D.D. Khokhlov – Junior Research Scientist, Scientific and Technological Center of Unique Instrumentation of RAS Е-mail: khokhlov.dd@ntcup.ru

The described study demonstrates that different isolated parts of the yolk show different changes in optical density during onehour monitoring of the embryo development from 32 to 33 stages. An increase from 24 to 25 or 26 pairs of body somites occurs in this period. The embryo length increases and separation of the tail from the torso begins. The yolk continues to actively change shape and become more pear-shaped, while there is an active movement of the yolk granules from the tail region to the central. In the head part of the embryo, the invagination of the eye glass anterior wall and the formation of crystalline placodes begin. It should be noted that until the 32 stage of development embryo stay motionless, and at the 33 stage, the beginning of movements in the embryo is observed. It means that in the transition from 32 to 33 stages of development there are certain changes in the structure of the head and tail sections of the embryo and in the yolk sac. The structure regularity of the spectra recorded in different isolated zones of the yolk sac of the developing loach embryo within 1 hour is presented. Analysis of the optical density spectra shows that the spectra of different local regions of the yolk sac have both certain similarities and differences. The changes of the optical density spectra in all four cases clearly indicate a transition from 32 to the 33rd stage of development at the 30th minute of observation. This transition represents one of the most important transformations in the biological system and, apparently, is due to the regulatory features of the central nervous system. In all analyzed areas of the loach embryo yolk sac the minimal values of spectral optical density observed at the moments of 30, 40, 49-50 and 58 min may indicate the synchronization of certain processes occurring in different areas of the embryo yolk sac. On the other hand, the presence of additional minimum values of the spectral optical density of egg yolk head region (4, 10, 36 and 44 minutes) may point at greater heterogeneity of biochemical processes that occur in this region. At the same time, the process of regular oscillations of the optical density for the yolk at all the studied points is noteworthy. A significant difference in the nature of light absorption for the yolk region in the vicinity of developing somites from other areas of the yolk is shown, which indicates a kind of polarization within the biological system. The monitoring results obtained using the non-invasive acousto-optic spectral imaging method at the intermediate stages of the embryo loach development give the same extended understanding of the dynamics of the processes occurring in time, as in the monitoring of other organs and tissues presented in the literature. This study may lead to a new understanding of the kinetics of the processes at the molecular level that ensures the development and may allow tracing the coordination of metabolic processes in the formation of a self-organizing biological system.

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