1. Pressures on the right and left sides of the tails of swimming bluefish were measured and found to have a range of +5·9 to −5·9 cm H20. The pressures were resolved into their forward and lateral vectorial components of force to allow calculation of forward and lateral force and power at speeds ranging from 0·26 to 0·87 m/s.

  2. The peak to peak changes in force of acceleration of the body, measured with a forward accelerometer averaged 209 g or 2·05 N at 0·48 m/s, and were compared with the maximum to minimum excursions of forward tail force averaging 201 g or 1·97 N at the same speed. The mean difference was 8 g, S.D. of the mean difference ±29, S.E. of mean difference ± 10 g.

  3. Mean tail thrust was calculated as the time average of tail force in the forward direction. It averaged 65 g, or 0·64 N, at 0·48 m/s. The mean forward power was 0·34 N m/s at 0·48 m/s. The drag of the gauges and wires accounted for 10% of this figure.

  4. The mean lateral power of the tail was 1·28 N m/s at a mean speed of 0·48 m/s.

  5. The propulsive efficiency of the tail, calculated as the ratio of forward power to forward plus lateral power, was found to be 0 20 S.D. ± 0·04, S.E. ±0·01 and was not related to speed. This suggests that 80% of the mechanical power of the tail was wasted. Turbulence in the water may have contributed to this large drag and low tail efficiency.

© 1978 by Company of Biologists
1978
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