Scanning electron microscopy of the heart of the climbing perch

The air-breathing climbing perch Anabas testudineus has two ventral aortas, one directs blood through well developed anterior gill arches into the suprabranchial chambers and back to the heart and the other sends blood through rudimentary shunt-like posterior arches and onto the systemic circulation. The sinus venosus is a thin-walled structure and lacks myocardial trabeculae. The atrium is similar to that of other teleosts and it is traversed by numerous myocardial trabeculae. There are no sinoatrial valves, whereas the atrioventricular aperture is guarded by one pair of large wing-shaped and two small cap-shaped valves. The ventricle is composed only of spongy myocardium and has numerous branching lacunae extending to the epicardium. The thick-walled bulbus arteriosus is lined with longitudinal ridges and this and the ventricular trabeculae may minimize mixing of respiratory and systemic flow while blood is passing through the heart. However, with the exception of the absence of sinoatrial valves and the ridged bulbar lumen, the heart of the climbing perch is essentially similar to that of most other non air-breathing teleosts.