The skeleton, support and movement

Buoyancy largely supports fish, reducing the role of the skeleton, which functions as an attachment for muscle involved in movement and in protection, as exoskeleton (scales, scutes, bony plates) and as endoskeleton (vertebral column, skull). The general organization of fish skeletons and their component parts are described, as well as bone and cartilage. The interesting occurrence of acellular bone, additional to cellular bone, in teleosts is considered. Fish show metameric segmentation with myotomes on either side of the vertebral column, the latter acting as a compression strut, preventing shortening. Myotome muscle is organized into linear units named sarcomeres which contract by means of protein fibres, myosin and actin, sliding past each other. Usually fish body wall muscles occur as a thin outer layer of aerobic red muscle, with an inner thick region of anaerobic white muscle. Interspecific variability in the relative roles of myotomes and fin musculature in swimming is discussed.