ATTITUDES EXPRESSING EMOTION 7 



for more than a second or two in this attitude of alarm, 

 and it was only because this perch was particularly 

 tame that he had the pluck to resent the tapping on the 

 glass. A wild fish would have rushed off, knocked its 

 head against the end of the tank, and then sulked on 

 the bottom. 



Most fish show their alarm by erecting their fins, 

 but a few, in addition, strike attitudes peculiar to 

 themselves. The cottus puffs out his cheeks ; the 

 blenny frequently, though not invariably, curls his 

 tail towards his head ; the carp bends the end of the rays 

 of the tail fin at right angles ; and in all probability 

 observation will show that most fish have some char- 

 acteristic way of showing their alarm. 



I have illustrated how a fish becomes pale with fear 

 but some tropical fishes actually change their colour. 

 This is due to the fact that fear makes the colour cells 

 in the skin contract, and the colour of the skin with 

 contracted cells is different from the same with relaxed 

 cells. 



In order to obtain photographic illustrations of the 

 attitudes and movements of fishes, it is necessary to 

 give a rapid exposure, usually one-hundredth of a 

 second. This is only possible when fish are photographed 

 in a glass tank, with a good light, but a wild fish with 

 this unusual illumination is too alarmed to be natural. 

 It is only after a fish is sufficiently accustomed to the 

 light to feed freely that photographs of attitudes are of 

 any value. It would be quite reasonable to question 



