6 VERTEBRATE RESPIRATION 



at rest is utilised in the pumping of air in and out of the lungs. 

 Accurate determinations of this figure have not been made for 

 fish but there is little doubt that it will be greater than 10 % and 

 may be as much as 25 %. Thus, if a trout increases its ventilation 

 4 times there is a 75 % increase in oxygen consumption although 

 there are no other apparent changes in its activity. When com- 

 pared with terrestrial vertebrates, fish therefore seem to be at a 

 distinct disadvantage from the respiratory point of view. One 

 feature in which they do have advantages, however, is that the 

 carbon dioxide can be removed from the respiratory system 

 much more easily because of its greater solubility in water and 

 the low concentration outside the fish. 



Further complications arise for fish because of the effect of 

 temperature on the oxygen content of the water and on the 

 metabolism of the animal. These effects are most striking in 

 fresh waters and the figures in Table 3 are for the oxygen con- 



Table 3 



Goldfish. The relationship between temperature, O2 content of 



the water and the ventilation volume necessary to satisfy 



the resting metabolism. (Data of Fry and Hart, 1948) 



sumption of a goldfish at different temperatures when at rest, 

 or swimming at constant speed. It can be seen that a seven-fold 

 increase in temperature raises the resting metabolism 28 times 

 but the oxygen available to the fish in unit volume of water 



