Morphological analysis of the fish heart ventricle: myocardial and connective tissue architecture in teleost species.

Light and scanning electron microscopy were used to study the structure of the heart ventricle in three species of marine teleost fishes: the hake (Merluccius merluccius), the angler fish (Lophius piscatorius) and the sea bream (Pagellus centrodontus). Our findings show the ventricle to be shaped differently in each species: tubular in the hake, saccular in the angler fish and pyramidal in the sea bream. From a structural viewpoint, interest was centered on two aspects: organization of the myocardial fibres and arrangement of connective tissue. In hake and angler fish ventricles, the myocardium was exclusively trabecular in nature, whereas the bream ventricle, in addition to trabecular myocardium, presented a thin compact layer. Muscle fibres showed precise patterns of organization at the level of the ventricular orifices. With the techniques used the intramyocardial connective tissue was detected in the following ventricular zones: i) at the level of subepicardial and subendocardial spaces, ii) surrounding the myocardial fascicles, and iii) surrounding individual myocardial cells. According to this structural study, the pyramidal ventricle of the fish should be considered as a ventricular pump with greater efficiency.