The venous circulation: a piscine perspective

Area of Science:

• Cardiovascular Physiology
• Comparative Physiology

Background:

• Vascular capacitance, the pressure-volume relationship of the circulatory system, is primarily managed by the venous vasculature.
• While crucial for terrestrial animals to prevent orthostatic blood pooling, its role in fish is linked to cardiovascular homeostasis, affecting venous return and cardiac output.
• Limited research exists on venous function in elasmobranchs, cyclostomes, and air-breathing fish compared to teleosts.

Purpose of the Study:

• To review venous haemodynamic concepts and neurohumoral control systems in fish.
• To emphasize venous responses to natural cardiovascular challenges in fish, including exercise, environmental hypoxia, and temperature changes.

Main Methods:

• The review synthesizes existing literature on vascular capacitance and its control mechanisms in fish.
• It discusses the measurement of mean circulatory filling pressure as an estimate of vascular capacitance.
• Focuses on neurohumoral regulation and responses to physiological stressors.

Main Results:

• Venous capacitance control is vital for cardiovascular homeostasis in fish, influencing venous return and cardiac filling pressure.
• Neurohumoral systems actively regulate the venous vasculature in fish.
• Fish venous systems exhibit distinct responses to exercise, hypoxia, and temperature variations.

Conclusions:

• Understanding venous capacitance in fish is essential for comprehending their cardiovascular regulation under various physiological conditions.
• Further research is needed, particularly in non-teleost fish species.
• Venous capacitance plays a significant role in fish adaptation to environmental and physiological challenges.