THE ALLIES OF THE PERCH: PISCES 



323 



important fresh-water families are the sunfishes (Centrar'chidce), 

 the perches (Per'cidce), and the catfishes (Silur'idce). Many of 

 the salmon and trout are inhabitants of fresh water, though 

 some of the larger species are marine, visiting fresh water 

 only to lay their eggs. The peculiar distribution of the few 

 lung-fishes which have survived the vicissitudes of geological 

 time has already been mentioned. When allied species of 

 animals are widely scattered over the globe in small separated 

 areas, the distribution 

 is spoken of as dis- 

 continuous. 



There are three 

 common divisions of 

 the ocean fauna, - 

 the littoral or shore 

 fauna, the pelagic or 

 open-sea fauna, and 

 the abysmal or deep- 

 sea fauna. The shore 

 fishes never venture 

 far into the open sea. 

 Among them are to 

 be included the large 



members of the salmon family already referred to. The pelagic 

 fishes are mostly hunters of other animals in the sea and are 

 strong swimmers, as befits their environment. Typical fishes 

 of this type are many of the sharks. 



The most peculiar forms belong to the deep-sea fauna. 

 There, of course, the conditions are unusual; life must be 

 adapted to an enormous pressure, to a low temperature (not 

 far above freezing), and to absolute darkness, except where 

 it is lit up by some phosphorescent animal. Hence the fishes 

 found in the deep waters are most bizarre, characterized by 

 uniformity of color-pattern, often black, though brighter 



FIG. 161. Deep-Sea Fish 

 (From Gunther's Fishes) 



