Heart structure of some deep-sea fish (Teleostei: Macrouridae)

The hearts of 29 species of macrourid teleosts were examined in this study. For the one species for which a length range was available ( Coryphaenoides (C.) rupestris ), the heart weight as a percentage of body weight was 0·059. This is similar to values for relatively inactive fish. The atrial myocardium was reduced and had only a sparse trabecular network. In some species it was surrounded by a highly developed epicardium, but in others there was interstitial connective tissue in the myocardium that may serve to strengthen this chamber. The ventricle was entirely spongy, and all species lacked an outer compact layer of myocardium and associated coronary vasculature. All the ventricles were sac-like in form. The bulbus arteriosus was highly complex, and in its proximal portion there was an endothelially-lined, inner tube surrounded by a spongy network of blood-filled spaces, outside which was an outer compact layer of smooth muscle and elastica. These features of the bulbus may prevent backflow of blood after ventricular systole. The endothelial cells lining the bulbus were usually PAS-positive and in some species contained acid mucopolysaccharides.