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Fig. 5. Factors affecting thunniform swimming biomechanics. (A) Contrasts of the
more fusiform body shape of the striped bonito, Sarda orientalis
(top), with the black skipjack's (Euthynnus lineatus) increased
anterior vertical thickness (from Graham,
1975). (B) Three-dimensional perspective for Sarda
(S) and Euthynnus (E) of similar size showing
structural features of a single myotome. The hatched area is the only aspect
of the myotome that would be visible in a skinned fish. Myotomes have anterior
pointing arms (APA) and cones (APC) and posterior pointing cones (PPC) and
connect to the vertebral column via the anterior (AOT) and posterior
oblique tendons (POT) within the horizontal septum. Lines on the surface of
APCs show how AOTs wrap around the APCs for force transfer. The tuna has
thicker, longer APCs and an anterior-medial red muscle (RM) mass (stippling).
In the bonito, with laterally placed RM, the AOT is longer than in the tuna.
As the bonito POT extends posteriorly to insert on vertebrae, it makes a
greater angle of incidence with the vertebrae than in tuna. Also illustrated
for Euthynnus are its left-side lateral artery (la) and vein (lv) and
its central rete (cr). Reproduced from Graham and Dickson
(2000).
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