A fish's skeleton is composed of cartilage or bone. Basically, the skeleton provides a foundation for the body and the fins, encases and protects the brain and the spinal cord, and serves as an attachment for muscles. It contains three principal segments: skull, vertebral column, and fin skeleton.
The meat or flesh covering the fish's muscular system is quite simple. All vertebrates, including fish, have three major types of muscles: smooth (involuntary), cardiac (heart), and striated (skeletal). Functionally, there are two kinds: voluntary and involuntary.
In fish, the smooth muscles are present in the digestive tract, the air bladder, the reproductive and excretory ducts, the eyes, and other organs. The striated muscles run in irregular vertical bands, and various patterns are found in different types of fish. These muscles compose the bulk of the body and are functional in swimming by producing body undulations that propel the fish forward. The muscle segments, called myomeres, are divided into an upper and a lower half by a groove running along the midbody of the fish. The myomeres can be easily seen if the skin is carefully removed from the body or scraped away with a knife after cooking. These broad muscles are the part of the fish that we eat. Striated muscles are also attached to the base of the fin spines and rays, and they maneuver the fins in swimming.
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