BODY FLUIDS AND CIRCULATION 



91 



TABLE 3.2 

 Blood Pressures of Fish 



therms of comparable size. Clark observes that the heart ratio (heart 

 weight over body weight) of a fish is much lower than that of mammals. 

 Since the oxygen requirements offish are only a fraction of those of warm- 

 blooded animals, a much smaller circulatory volume per minute is ade- 

 quate for fish metabolism. 



Cardiac activity in fish, as in other vertebrates, is subject to autonomic 

 control, resulting in changes in blood pressure. With increase of heart 

 rate there is a rise of blood pressure and a decline of pulse pressure, as the 

 arteries become increasingly distended. The circulation rate depends on 

 the volume output of the heart per beat (stroke volume), and the frequency 

 of heart beat, and as the latter increases there is an increase in the velocity 

 of blood flow. Measurements made on the eel {Anguilla anguilla) show that 

 the blood leaving the heart takes from 12 to 60 sec to reach the various 

 posterior veins. 



