Intimal thickening of coronary arteries in the rabbitfish, Chimaera monstrosa L. (Chondrichthyes: Holocephali)

This study is the first to report the occurrence of intimal thickening of coronary arteries in a holocephalan, namely the rabbitfish, Chimaera monstrosa. The sample studied consisted of five hearts from rabbitfish with body weights ranging between 12 g and 1116 g. The specimens were fixed in formalin, in methanol:acetone:water (MAW), or in paraformaldehyde and were examined by brightfield and polarization light microscopy. Coronary arteries from three larger animals displayed focal intimal thickenings, which were located in the left main coronary artery trunk, at the level of the cono-ventricular junction, and in several intramyocardial ventricular arteries. The vascular changes were characterized by myointimal proliferation, breakage or absence of the inner elastic lamina, and, in one case, by increased collagen within the myointimal proliferation. Taking into account the severity of the coronary arterial changes, their location, and the body weight of the affected animals, we conclude that (1) these changes are age-related in the rabbitfish and (2) local intense mechanical tension seems to be an important factor in their formation in this species.