Unconstrained and noninvasive measurement of bioelectric signals from small fish

Abstract

Recently, the technique of fish bioassay has attracted attention as a method for constant monitoring of aquatic contamination. The respiratory rhythms of fish are considered to be an efficient indicator for the monitoring of water quality, since they are sensitive to chemicals and can be measured indirectly from the bioelectric signals generated by their breathing. However, no method has yet been established to measure signals in small free-swimming fish. In this article, we propose a system to measure bioelectric signals in small fish and monitor the frequency component in real time. To cover the large measurement range required in a free-swimming environment, the signals are measured using multiple electrodes. Further, the system focuses on the frequency component of the signal to assess the condition of the fish using frequency analysis and a band-pass filter. Experiments were conducted with the purpose of enabling remote sensing and environment estimation. First, it was verified that the measured signals were synchronized with the breathing of the fish. Then, a remote sensing experiment was performed using medaka (Oryzias latipes) that were allowed to swim freely in a measurement aquarium. The results confirmed that bioelectric signals which were synchronized with breathing could be measured in unconstrained and noninvasive conditions.