The Design of Fluid Transport Systems: A Comparative Perspective

Animals pump prodigious quantities of fluids within or through their bodies in conjunction with their normal activities. A human heart pumps the equivalent of 8.5 percent of the body’s volume per minute at rest, and 34 percent of the body’s volume per minute during strenuous exercise. Such high rates are not cheap; about 15 percent of a human’s resting metabolic rate goes into maintaining the circulation of the blood (16). Humans are typical mammals in this regard, but mammals, as might be inferred from their profligate energy consumption, maintain high relative rates of circulation compared to other vertebrates. A dogfish’s heart pumps only about 2 percent of the animal’s body volume per minute (9). A typical fish invests about 5 percent of its resting metabolic rate in driving the circulation, but 22%–27% of the resting metabolic rate is required in the icefish, Chaenocephalus aceratus, which partially makes up for its lack of hemoglobin by increased perfusion (22, 23).