Non-invasive recording of heart rate and ventilation rate in rainbow troutduring rest and swimming. Fish go wireless!

Resting heart rates and ventilation rates in rainbow trout Oncorhynchus myk iss at 15 degrees 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 bioe lectric potentials generated by the fish in the water and was based on an a rray of six silver-silver chloride electrodes covered with agar-gel, which provided a better signal-to-noise ratio than in previously described system s, and allowed the determination of heart rate and ventilation rates at dif ferent 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 a lso considerably larger than in earlier studies (2.4- and 2.0-fold, respect ively). Two main conclusions result from this work: (i) short recovery time s under 48 h after anaesthesia and surgery are unlikely to provide truly re sting heart rates and ventilation rates in trout at 15 degrees C; (ii) hear t rate regulation during exercise is more important than previously thought and might account for a larger proportion of the increase in cardiac outpu t observed in swimming trout. (C) 2000 The Fisheries Society of the British Isles.