Advantages and Disadvantages

Question

What are the advantages and disadvantages with a simple circulatory system (like the ones fish have)?

Answer 1

The tradeoff between simple and complex circulatory systems is between complexity and efficiency. A simple system like that in fish has a single continuous loop with only two heart chambers and no need for separation of oxygenated and deoxygenated blood in the heart. Thus, it consumes less energy, has fewer points of failure, and is easier to maintain when compared to more complex systems (e.g. fewer valves, less complex coordination of the heart pumping mechanism). However, simple systems are less efficient at distributing blood throughout the body, which reduces amount of oxygen received by certain organs and tissues and thus the organisms' overall metabolic capacity. This is why warm blooded (which require higher metabolic capacity) have more complex circulatory systems, whereas cold-blooded animals like fish do not require circulatory systems with that level of complexity/efficiency.