Acceleration rates, analyses of body movements, and pertinent anatomical features are given for various members of the Scombridae, Istiophoridae, and Xiphiidae and are discussed in light of the modern work on smaller freshwater teleosts and marine cetaceans.

Acceleration values up to 43.1 m/sec2 are given for Thunnus albacares and Acanthocybium solanderi. Nearly 100% of the propulsive thrust comes from the caudal fin. There are two main intervertebral joints which are concerned with locomotion, a pre-peduncular and a post-peduncular joint with the body and peduncle held almost stiff, a condition similar to that described for marine cetaceans. The caudal fin achieves its highest transverse verse speed near or past the axis of progression and the fin's maximum angle of attack occurs before the fin crosses the axis of progression. The caudal fin's angle of attack has an average value of 32.4° as the fin crosses the axis of progression and the average value for all observed fin positions is 29°. Values as high as 100° were attained. The aspect ratio (span2/surface area) of the caudal fin ranges from 10.26 (Istiophorus greyi) to 4.19 (Xiphias gladius). The higher values approximate those of efficient, high speed airfoils.

The positions of the joints and the rigidity of the vertebral column are discussed for the Scombridae, Istiophoridae, Xiphiidae, and Lepidocybium flavo-brunneum. It is suggested that the retention of autonomous epurals, hypurals, and uroneurals functions to allow camber in the otherwise fused caudal skeleton. The bony peduncular keel is shown to act as a pulley for the great lateral tendons as well as to somewhat stiffen the peduncle and to serve as a support for the fleshy peduncular keels.

Data concerning the shape, length, origin, insertion, and action of the ∑-shaped myomeres are given for the various fishes. Attention is focused on the relative role played by the red and white muscle, the tendons, and the intrinsic caudal musculature in locomotion.

A subordinal classification is presented for the scombroid fishes based upon some of the data presented in this study.



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