The rainbow trout, Salmo irideus, and sockeye salmon, Oncorhynchus nerka, on which a radiotransmitter was mounted, were allowed to swim in a stream and the ECG information was conveyed over wireless transmission. The velocity of the current was controlled by means of opening and closing a sluice at the lower reach of the stream.
The heart rate, the beats per minute rate, during free swimming remained unchanged and maintained a nearly settled frequency, independent of the acceleration and deceleration of water current in which the fish was free to traverse.
LUTZ's experiment on cardiac reflex was re-examined by increasing and decreasing the water supply to the gills of carp, cyprinus carpio. An increase in the rate of water to the gills caused an increase in the heart rate in so far as the fish was placed in a state of asphixia, being exposed to the air. The nature of this result did not exactly fit the case when the fish was placed in an aquarium and its gills bathed by the water.
The rate of heart beat during free rapid swimming was considered to be determined by the particular speeds necessory to be sustained during periods of swimming, a cruising speed, in ambient water temperature, and not by the rate of water flow through the mouth on inspiration.