Аннотация:Noninvasive registration and adequate analysis of response of living systems to low energy physical stimuli play an important role in contemporary biological and biomedical research. In this paper we discuss the possibilities of laser Doppler microscopy (LDM) application for the study of light irradiation and thermal effects on animal organisms. Fish embryos are shown to fit many requirements related to the performance of experiments in clearly defined conditions. LDM yielding quantitative data on the dynamic response of the embryos to temperature variations and light irradiation is proved to be an adequate diagnostic technique. A fringe- mode sign-sensitive LD microscope was used to monitor the alterations of blood flow in fish embryos. Measurements were performed with spatial resolution as small as 10 micrometers in real time scale. Experimental data on the biological effects of thermal and nonthermal light stimuli on different fish species are presented.