MYOCARDIAL FIBER AND CONNECTIVE-TISSUE ARCHITECTURE IN THE FISH HEARTVENTRICLE

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 co nsists of mixed compact and trabeculated myocardium. In sedentary and benthonic species, the ventricle is saccular and the myocardium is ent irely trabecular. However, in elasmobranchs the myocardium is always m ixed, 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 myocardiu m, the fiber bundles show an orderly arrangement within the ventricula r walls, and the intramyocardial connective tissue provides a scaffold ing that supports muscle fascicles, blood vessels and myocytes, and th us plays a role similar to that of the connective tissue in the mammal ian heart. Differences in the patterns of myocardial fiber and connect ive tissue architecture were also observed between teleosts and elasmo branchs. Regardless of the species and shape of the ventricle, the tra beculated myocardium always displays an anarchic arrangement-except fo r zones near the ventricular orifices, where it may play an active rol e 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 ventric les which are comprised entirely of trabeculated myocardium. (C) 1996 Wiley-Liss, Inc.