134 American Fisheries Society 



II. THE SENSES OF FISHES. 

 The sense organs of animals are sometimes divided 

 into two groups— surface receptors which take note of 

 objects in contact with them and distance receptors 

 which are affected only by vibrations or emanations from 

 distant objects. Amongst fishes the organs of touch, 

 temperature and taste are surface receptors while those 

 of smell, hearing and sight are distance receptors. Be- 

 sides these senses fishes have another not possessed by 

 man and to be presently referred to. 



A The Senses of Touch and Temperature need 

 not long detain us, for we know but little about them 

 in fish. Parker (1910b), has shown that when the salt 

 water dogfish {Mustelus canis) , is touched in particu- 

 lar regions of the body there result corresponding move- 

 ments of the fins or other parts. These are such as 

 either to turn the animal away from the object touch- 

 ing it or to brush away the irritation or to close the 

 cloacal opening or the eye. The fish has therefore a 

 sense of touch over the whole surface, and by means 

 of it is able to locate with some accuracy objects that 

 come into contact with it and to make the movements 

 necessary to avoid injury from these objects. 



That fish are very sensitive to slight differences in the 

 temperature of the water is known from the work of 

 Shelford (1915). He arranged long troughs in which 

 the water at the middle was of intermediate temperature 

 while it became gradually warmer toward one end and 

 colder toward the other. Fishes were introduced into the 

 middle of the trough and could then swim toward either 

 end. Each kind showed preference for water of a cer- 

 tain temperature and when, in swimming along the 

 trough, it encountered water of different temperature it 

 tended to turn back. By noting the point in the trough 

 at which various fish turned Shelford found that a differ- 

 ence in temperature of as little as five-tenths of a degree 

 centigrade might cause the turning. He believes that 

 fishes are sensitive to temperature differnces as little as 

 two-tenths of a degree centigrade. Michael (1908), has 



