Form, function and control of the Vasculature

This chapter summarizes the form, function, and control of the blood vasculature in fish. It starts with a general overview of the gross anatomy of the vascular system. We then turn to the arterial vasculature and the hemodynamic principles governing vascular resistance and arterial blood pressure, including a summary of the main local, neural, and hormonal systems controlling arterial resistance. The highly specialized vascular system of the gills (i.e., the branchial circulation) is covered in a separate section where we describe their complex microvascular arrangements, as well as the control mechanisms of both the arterioarterial ("respiratory") and arteriovenous pathways. The chapter closes with a comprehensive overview of the venous vasculature. This includes the hemodynamic principles determining venous return, the importance of central venous blood pressure for cardiac performance, and the neurohumoral control mechanisms of venous capacitance and compliance. Finally, we discuss the importance of venous hemodynamic changes during integrated cardiovascular responses such as exercise and barostatic reflexes, and in response to changes in environmental variables including temperature, oxygen availability and salinity. While the chapter, by necessity, is biased toward teleosts due to the more abundant literature for that group, information on elasmobranchs, cyclostomes, and air-breathing fishes is also provided to highlight similarities and differences among the major groups of fish.