GEMBALLA, Sven; TREIBER, Kerstin: Myoseptal architecture of a cruising specialist and an accelerator � Are different modes of locomotion in Scomber and Channa driven by differently structured myosepta?

Investigations carried out on myoseptal architecture have considered accelerators and locomotor generalists but have neglected cruising specialists. We present the first comparison of the myosepta of a cruiser (Scomber spec.) and an accelerator (Channa spec.) in order to gain insight into functional significance of myoseptal structures. Descriptions of myoseptal fibre architecture are based on microdissections and polarized light microscopy. We found considerable differences between the myoseptal tendons in the cruiser Scomber and the accelerator Channa. In Scomber the elongated and thick myorhabdoid tendons in the flanking parts and the lateral bands in the sloping parts are more prominent. Epineural tendons are absent in Scomber. Electromyographic and kinematic studies in mackerels indicate that muscular forces are generated anteriorly and transmitted posteriorly. We found this fact to be reflected anatomically: Lateral bands and myorhabdoid tendons of the posterior myosepta are elongated and oriented almost longitudinally. Thickness and mechanical coupling of these elements increases posteriorly resulting in the strong tendons of the caudal peduncle. The tendons formerly described as �Great Lateral Tendon� and �Medial Caudal Tendon� are identified as lateral bands of the posteriormost epaxial and hypaxial myosepta; other tendons attaching to the caudal fin rays are identified as myorhabdoid tendons of the posteriormost epaxial and hypaxial myosepta.