...No, it is just his heart beating.

There are several types of heart rate measurement methods that are based on different principles. In both humans and crayfish, the principle of measuring reflected infrared light is used. In humans, the sensor looks like a finger peg that you get in the hospital. In the case of the crayfish, then as a small box with wires attached to the back of the crayfish. Both devices monitor cardiac activity. In crayfish, cardiac activity is monitored because its change reflects changes in the quality of the water in which the crayfish lives. This principle is technically called bio-indication and crayfish is therefore used as a rapid bioindicator of the occurrence of undesirable substances in water.

There are limitations to measuring cardiac activity using infrared light, so researchers from the Laboratory of Signal and Image Processing, along with researchers from the Acoustics Laboratory at University of Le Mans, have been looking for new ways to monitor cardiac activity. The heart distributes blood across the body of the crayfish by mechanical contractions. These contractions cause vibrations that correspond in frequency to the heartbeat. Therefore, a sensitive accelerometer was placed on the crayfish, which allows you to measure the vibrations of objects. The accelerometer records all movements of the object and converts them into an electrical signal. So if something vibrates regularly, the signal will take a periodic form.

This procedure not only makes it possible to measure the cardiac activity of the crayfish, but also makes it possible to detect the movement of the crayfish (the periodical signal is lost). This is an advantage over the current infrared solution, which must use a camera to detect motion.

Detail information can be found in the original paper Novak, A., Cisar, P., 2020. Crayfish heart rate monitoring with an accelerometer. Ecological Indicators 111: 105993. (IF 2018 = 4,490; AIS 2018 = 0,899).

The signal of accelerometer for the cardiac activity of crayfish. First 15 seconds corresponds to the cardiac activity on non-moving crayfish. Last 15 seconds corresponds to motion of the crayfish.

Accelerometer placement on the back of crayfish.