Myocardial fiber and connective tissue architecture in the fish heart ventricle

Abstract

We used dissection, light and scanning electron microscopic techniques to analyze the arrangement of myocardial fibers and connective tissue in the ventricular walls of the fish heart. In teleost fishes with an active, pelagic lifestyle, the ventricle is pyramidal in shape and consists of mixed compact and trabeculated myocardium. In sedentary and benthonic species, the ventricle is saccular and the myocardium is entirely trabecular. However, in elasmobranchs the myocardium is always mixed, regardless of the species's lifestyle, although the shape of the ventricle is pyramid-like in more active fishes (e.g., the mako shark). In all species of teleosts and elasmobranchs with compact myocardium, the fiber bundles show an orderly arrangement within the ventricular walls, and the intramyocardial connective tissue provides a scaffolding that supports muscle fascicles, blood vessels and myocytes, and thus plays a role similar to that of the connective tissue in the mammalian heart. Differences in the patterns of myocardial fiber and connective tissue architecture were also observed between teleosts and elasmobranchs. Regardless of the species and shape of the ventricle, the trabeculated myocardium always displays an anarchic arrangement except for zones near the ventricular orifices, where it may play an active role in valve dynamics. The architecture of the connective tissue in the trabeculated myocardium is irregular, poorly defined, and less evident than in compact myocardium, specially in tubular and saccular ventricles which are comprised entirely of trabeculated myocardium. © 1996 Wiley-Liss, Inc.