  In undulatory swimming of fish, muscles contract sequentially along the body
to generate a bending wave that pushes against the water and produces thrust.
Here, we use a 3D computational fluid dynamics model coupled to the motion of
the fish with prescribed deformation to study the basic mechanical quantities
along the fish's body: force, torque, and power. We find that forces on the
bodies of both the anguilliform swimmer and the carangiform swimmer are
dominated by reactive forces; furthermore, the force on the caudal fin of the
carangiform swimmer is dominated by drag-like forces. The torque exhibits a
wave pattern that travels faster than the curvature wave in both the
anguilliform and carangiform swimmers, but the wave speed is even higher for
the carangiform swimmer. The power output for the anguilliform swimmer is
concentrated on the anterior half of the body and is significantly negative on
the posterior side of the body. In contrast, most of the power is generated by
the posterior part of the body before the peduncle for the carangiform swimmer.
The results explain the differences in the observed electromyography patterns
in fish with different swimming modes and explain the tendon function in
carangiform swimmers.
