How fish muscles work from the molecular to the whole organ level is a lecture from the University of Southern Maine that gives focus to this learn node. A basic concept for the subject is that:
Two contrasting behaviors: The first is steady swimming at slow and intermediate speeds using low amplitude axial undulations (i.e. the side to side displacement of the body is small). The second is burst swimming and escape responses using high amplitude axial undulation. In the escape response, a fish bends into a C-like posture then whips its tail in the opposite direction, accelerating a mass of water behind the fish, which causes the fish to accelerate forward. The key is that body bending is small in steady swimming and large in bursts and escapes. Also, the escape response can be very fast, that is less than 1/10th of a second.
The toadfish is an important fish muscle specimen because it has been found that its swim bladder muscles are the fastest twitching muscles in the vertebrate world. The image by Robert Golder shown here is from an article at the Marine Biological Laboratory on this talented but ugly fish. Several articles at the St. Andrews University website of its Fish Muscle Research Group provide the latest ideas and theories in this important subject for mechanics, anatomy, genetics, and aquaculture.