Gram for gram fish have more muscle than any other vertebrate, a male salmon or tuna can be nearly 70% muscle, which is one reason why fish are so good to eat. The muscles of fish are layered rather than bundled as in the other vertebrates. Each segment, or sheet, of muscles is called a myomere or myotome and is separated from its neighbor by a sheet of connective tissue. Other sheets of connective tissue, called septa (pl =septum) occur along the vertical midline of the body separating the muscles of the left and right sides of the body, and horizontally separating the muscles of the upper and lower halves of the body. The muscles of the upper half of the body are called 'epaxial' and those of the lower half are called 'hypaxial'. Salmon are a particularly good fish for studying the basic shape of fish muscle because the coloration of their muscles allows you to see the edges of each myotome, as in the picture above and the photos below.