[Study of circadian activity in the crayfish Pontastacus leptodactylus during their multimonth stay in the river water flow].

By the method of non-invasive on-line recording and processing of photoplethysmograms of testaceous invertebrates, the circadian rhythm of cardiac activity was studied in the crayfish Pontastacus leptodactylus by recording for several months the heart rate (HR) and stress-index (characteristics of variational pulsometry). The crayfish were kept in the natural running water in the regime of natural illumination alteration (the first group) or at constant artificial illumination of low intensity (the second group). The circadian rhythm was more frequent and more distinct in crayfish of the first group.