AQUATIC VERTEBRATES 



373 



this ; if placed on sand the specks on its body will be quite small, but if 

 placed on gravel the specks will be larger to blend with the larger rock 

 particles. One was placed on a black and white tile and actually devel- 

 oped a rough pattern of checks corresponding in size to the tile. This is 

 possible because of the presence of small color bodies in the skin which 

 can be expanded or contracted to make any area of the skin dark or light. 

 Many small tropical fish show brilliant coloration and when seen in a 

 fish bowl or aquarium might appear quite conspicuous. However, when 

 seen in their natural surroundings of brilliantly colored coral, seaweed, 

 and other tropical forms of life, they blend nicely and the brilliant colora- 

 tion is a protection. 



Photos by Winchester 



Fig. 25.6. Protective coloration in the flounder. The flounder is able to change the 



pattern and coloration to blend with its surroundings by expanding or contracting 



pigmented bodies in the skin. Even when placed on such an unnatural surface as that 



on the right it is able to change until it rather closely resembles its surroundings. 



In one group of marine fishes the paired fins are enlarged and may be 

 used in gliding through the air over the surface of the water. These 

 are the flying fish, but since there is no flapping of the fins they are actu- 

 ally gliders rather than fliers. When an enemy goes after them they 

 swim rapidly to get a start and then flip themselves out of the water and 

 sail through the air for distances as great as an eighth of a mile. 



Another interesting means of protection is found in the electric eel. 

 This large eel, which grows to a length of several feet, is found in South 

 American rivers and lakes. When irritated, it is capable of giving out a 

 shock that will knock down a person standing in the water nearby. 

 Wires can be run from one of these eels to an electric light bulb and 

 when the eel is disturbed the bulb will light up. 



The porcupine fish, found in tropical waters, does not need any of the 

 means of protection described. Its body is covered by sharp spines, 

 which normally lie flat on its body, but when in danger the fish will in- 

 flate itself with either water or air so that it expands into a tight ball and 

 the spines stand out to discourage any animal that might wish to eat it. 

 If a large animal, such as a shark, should be so hungry that it swallowed 



