1Graduate Course of Marine Life Sciences, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, 2Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477
The heart rate of kuruma shrimp Marsupenaeus japonicus during exercise was examined in a flume tank based on swimming endurance trials in a speed range of 17.7-33.9 cm/s, and by electro-cardiogram (ECG) monitoring. With increased swimming speed, endurance time was shown to decrease, showing a sustained speed of 23.9 cm/s by swimming curve analysis. Heart rate in the control phase could be divided into three groups according to the peak mode of beat per minute; the dominant group showed a heart rate of 90-100 beats/min, and the lower level group was 40-50 beats/min. The high level group showed a rate exceeding 100 beats/min. When the shrimp were forced to swim against the flow, heart rate increased to the range of 80-210 beats/min. However, the magnitude of increase was not proportional to the speed. The increment ratio of heart rate for the exercise phase against the control in each individual revealed a trend of higher values for the low control heart rate group, and lower values for the high heart rate group. The variation of increment ratio was observed to be larger at higher speeds than the sustained speed.