Background. Assessments of the efficacy of anaesthetics are usually based on observations of fish behaviour or changes in blood parameters. In this study we attempted to assess the process of anaesthesia, caused by MS-222, based on the measurement of heartbeat and respiratory frequency. Materials and methods. The effect of four concentrations of MS-222 (75, 100, 125, and 150 mg · L-1) on heartbeat and respiratory frequency of common carp, Cyprinus carpio L., were studied using ECG. Concurrently (during general anaesthesia) fish behaviour was also observed. Results. The behavioural reactions were similar for all four treatments. The first symptom was agitation followed by sedation, loss of equilibrium, and deep anaesthesia. Small differences were observed during initial contact of fish with the anaesthetic. The ECG analysis, however, revealed significant differences in heartbeat and respiratory frequencies related to the concentration used. Irrespective of the MS-222 concentration used, the recovery time was similar in all treatments and did not exceed 5 minutes. Conclusion. The ECG method can be an important and objective tool supplementing the data acquired during visual observations of responses to anaesthesia. Its major advantage is the comparativeness of data.

fish, Cyprinus carpio, common carp, anaesthesia, ECG, respiration, MS-222, tricaine, heart rate