The dynamics of the numbers of the decapod crustacean populations depends essentially on the anthropogenous load on inner reservoirs. This process affects the most substantially the crayfish species Astacus astacus L. that is aboriginal for the North-West of Russia. The sensitivity of these crayfish to changes of the water quality in the ecosystems has been noted by many authors [1, 11, 15]. For an ecophysiological monitoring of the reservoirs as well as for a nature-protective and aquacultural activity necessary, is necessary to have methods and means of determination of quantitative parameters of responses of animal life-providing systems, for example, the cardiovascular system. In the present work, a new non-invasive technique is proposed for recording parameters of the crayfish heart activity. The method is based on measurement of the laser emission of the near-infrared diapason, which is scattered in the reverse direction. This paper describes the instrumental part of the complex and exposes some preliminary data obtained with the aid of the used method of recording the crayfish heart activity. This method is shown to permit not only recording the crayfish heart rate under conditions of free behavior, without any harm to the animals, but also tracing changes of the shape and amplitude parameters of the response, which characterize the animal state.