Mechanical properties of fish backbones in lateral bending and in tension

The mechanical properties of the backbones of the Norfolk spot, a subcarangiform swimmer, and the skipjack tuna, a thunniform swimmer, have been compared in lateral bending and in tension. In both testing modes the skipjack backbone is significantly stiffer than that of the spot. In addition, the skipjack backbone contains three distinct regions of differing flexibility in bending, while the spot backbone is uniform in its properties in bending all along its length. Because the skipjack tuna's backbone is extremely stiff in tension, it appears that compression of the intervertebral joints may be more important during lateral bending of this fish compared to the Norfolk spot. This study demonstrates that for at least the fishes tested here, the properties of the backbone in lateral bending are well tuned to the particular swimming style used.