146 The Life Story of the Fish 



The normal rapidity of these movements varies. The hu- 

 man being takes from 20 to 25 breaths a minute. In com- 

 parison, the rate in fish varies from as low as 12 per minute 

 in the wrasses to as high as 150 in the minnows. In the brook 

 trout it is between 40 and 50. Under stress, such as when the 

 fish puts forth unusual exertions, or when the oxygen con- 

 tent of the water becomes low in an aquarium with too many 

 fish and insufficient aeration, the rate is accelerated and the 

 fish "pants." 



As the water passes through the gill chambers and out 

 through the gill openings it is easy to see that the current 

 might carry with it particles of food from the mouth which 

 might injure the delicate gill filaments. To guard against 

 this the gill arches are equipped with straining devices known 

 as gill rakers. In fish which eat large animals the rakers are 

 nothing more than knoblike protuberances on each side of 

 each arch. In the herring they are fine, almost hairlike out- 

 growths, acting more as a sieve to prevent the escape of the 

 minute organisms on which it feeds than as a protection for 

 the gill filaments. In general, however, they are designed 

 to prevent the food from interfering with the breathing, just 

 as the valve called the glottis in our throat is designed to 

 prevent food from getting into our windpipe. That these 

 safety devices sometimes fail to work, in fish as well as in 

 men, is evidenced by the body of a twenty-pound striped 

 bass found with a three-pound carp stuck in its gill opening, 

 its wiggling tail still protruding from its captor's mouth. 

 The would-be diner had suffocated, but the intended dinner 

 was still alive. 



Some people are under the impression that it is the 

 oxygen constituent of water which the fi,sh breathes. Their 

 inference is not illogical, since water, as we all know, is 

 composed of one part of oxygen to two parts of hydrogen. 

 What they fail to take into account is the fact that water 



