The horizontal septum: Mechanisms of force transfer in locomotion of scombrid fishes (Scombridae, Perciformes)

Abstract

We describe the complex shapes of myomeres and myosepta in the mackerels and tunas (Scombridae: Teleostei), and we reveal the orientation of two major systems of collagen fibers in myosepta and horizontal septa with respect to points of attachment to skeleton and skin. Our goal is to identify the likely pathways of the transmission of muscle forces during locomotion. Our primary conclusions are (1) that the collagen fibers of myosepta, horizontal septa, and skin are the organs that transfer locomotor forces from the contraction of myomeres to the backbone and caudal fin during locomotion, and (2) that locomotor muscle pulls against a three-dimensional structure of tendons, septa, and skin that is kept in tension by the radial expansion of the contracting muscle. The main horizontal septum is formed by the convergence of myosepta and is likely to be the major transmitter of muscle force to the axial skeleton. The geometry of the myomeres, the position of red muscle, and particularly the geometric conformation of crossed-fiber arrays of collagen in the main horizontal septum suggest specific mechanisms for the transfer of muscle force to the backbone among scombrid fishes. Morphometrics and the construction of physical models help us to identify musculoskeletal mechanisms of locomotion, and we present two quantitative models of locomotor mechanics in fishes. © 1993 Wiley-Liss, Inc.

Unilateral perivertebral fibrosis associated with lordosis, kyphosis and scoliosis (LKS) in farmed Chinook salmon in New Zealand

“…In the presently described Chinook salmon, the inflammation and fibrosis was most consistently present close to the insertion of the horizontal septum. The horizontal septum is considered to be the major transmitter of muscle force to the axial skeleton (Westneat et al 1993). Therefore, it is possible that intense muscular activity could damage the connective tissue within, and adjacent to, the horizontal septum, resulting in the observed inflammation and subsequent reparative fibrosis.…”

A functional analysis of myotomal muscle-fibre reorientation in developing zebrafishDanio rerio

“…Comparative overviews of the myotomal muscle-fibre arrangement in Actinopterygii and Selachii have been published (Wainwright, 1983;Gemballa and Vogel, 2002), and the morphology of the myomeres in scombroid fishes has been described (Westneat et al, 1993). In bony fish (including our present focus, the zebrafish), each myomere is folded into an anterior cone, a dorsal posterior cone and a ventral posterior cone.…”

“…Medial portions of the ESP and HSP are about parallel to the horizontal septum and the longitudinal series of myosepta form connective tissue multilayers in this region (the medial multilayers of the epaxial and hypaxial sloping parts of the myosepta (MESP and MHSP, see Fig.·8C). Wainwright described these layers as epaxial en hypaxial horizontal septa (Wainwright, 1983), but they have also been called secondary horizontal septa (Westneat et al, 1993).…”

Swimming performance studies on the eastern Pacific bonitoSarda chiliensis, a close relative of the tunas (family Scombridae) I. Energetics

“…This is paradoxical because tuna specializations, including a high degree of body streamlining, a unique RM position, tendon arrangement, thunniform swimming mode and endothermy, have all been hypothesized to augment aerobic swimming performance and presumably swimming efficiency (Carey and Teal, 1966;Fierstine and Walters, 1968;Graham, 1975;Johnston and Brill, 1984;Westneat et al, 1993;Altringham and Block, 1997;Dickson, 2000, 2001;Donley and Dickson, 2000;Ellerby et al, 2000;Altringham and Shadwick, 2001;Dowis et al, 2003).…”