Non‐invasive recording of heart rate and ventilation rate in rainbow trout during rest and swimming. Fish go wireless!

Resting heart rates and ventilation rates in rainbow trout Oncorhynchus mykiss at 15°C are 31·8±1·8 beat min −1 and 53·1±3·7 breaths min −1 , respectively. The non‐invasive recording system picked up the bioelectric potentials generated by the fish in the water and was based on an array of six silver‐silver chloride electrodes covered with agar‐gel, which provided a better signal‐to‐noise ratio than in previously described systems, and allowed the determination of heart rate and ventilation rates at different swimming speeds up to 21 s −1 . In concert with the lower rates, the scope for changes in heart rate and ventilation rate during swimming was also considerably larger than in earlier studies (2·4‐ and 2·0‐fold, respectively). Two main conclusions result from this work: (i) short recovery times under 48 h after anaesthesia and surgery are unlikely to provide truly resting heart rates and ventilation rates in trout at 15°C; (ii) heart rate regulation during exercise is more important than previously thought and might account for a larger proportion of the increase in cardiac output observed in swimming trout.