ABSTRACT
Three types of muscle cells are present in the muscular tissue of fishes: skeletal, cardiac musculature, and smooth musculatures. Skeletal muscle fibers are multinucleated syncytia that originate and insert on the bones of the skeleton. The fish contains two types of skeletal muscle types: red and white that have different degrees of vascularization and myoglobin content. These two kinds of muscles are involved in two kinds of swimming activity. Cardiac muscle fibers consist of anastomosing and branching cardiomyocytes. At sites of end-to-end contact are the intercalated discs. The specially modified conduction pathways (Purkinje fibers) seem to be lacking in fish hearts. Smooth muscle fibers usually form the contractile portion of the walls of most viscera and the tunica media of the arteries and veins. The cells (leiomyocytes) of smooth muscle are spindle-shaped structures without striations. The leiomyocytes are placed close together, forming layers or sheets, although single cells may be formed. The cell contains delicate contractile myofilaments.
The muscular tissue is composed of cells that specialize in mechanical work. Three types of muscle cells are present in the muscular tissue of fishes: (1) the skeletal musculature, consisting of striated, unbranched, and voluntary fibers; (2) the cardiac musculature, consisting of striated and branching involuntary fibers; and (3) the smooth unstriated, involuntary musculature.
