The blue-green coloration of the blood plasma in some marine fishes, which is attributed to a protein bound tetrapyrrol (biliverdin), is an anomaly in vertebrates. 2. Recent studies have shown that biliverdin not only occurs in many fish, but is also present in the blood of tobacco hornworm, the wings of moth and butterfly, the shell of bird eggs, the serum and egg of frog, the placenta of dog and in the blood of humans suffering from hepatic diseases. 3. In this review, we begin with a historical account of the description of the presence of blue-green blood plasma in fish, and then consider the biochemistry, metabolism, physiology, and the ecological implications of biliverdin in fish. 4. A comparative description of the occurrence of biliverdin in fish and other animals is presented. 5. The mechanism of accumulation of biliverdin in fish blood and its evolutionary significance are also considered. It is suggested that this process may serve as a useful model for further research on bile pigment metabolism in other animals.
