Circulatory Anatomy in Bimodally Breathing Fish

SYNOPSIS. The development of air-breathing organs in bimodallybreathing fish has necessitated a degree of vascular remodellingin order to enhance gas exchange and support other homeostaticactivities. Macrocirculatory changes include several plumbingschemes that allow perfusion of the gills, air-breathing organ,and systemic circulations in a variety of in-parallel and in-seriesarrangements. The incorporation of structural adaptations designedto minimize admixture of oxygenated and deoxygenated blood intransit through the heart as well as vascular shunts furtherincreases the efficiency of the gas exchange process. A numberof anatomical modifications in capillary architecture and endothelialcell structure are found in air-breathing fish and appear tobe unique to these vertebrates. The physiological significanceof the microcirculatory adaptations remains, to a large extent,speculative.