330 



GENERAL ZOOLOGY 



Geographical Distribution of Fishes. A simple and seem- 

 ingly natural classification of fishes, as regards their hab- 

 itat, is a division into fresh-water and marine forms. This 

 will serve our purpose if it be remembered that there has 

 been much interchange of species between the two. 



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 ven- 

 ture 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 

 colors are sometimes developed ; by modifications of the 

 eyes, which are either very large in proportion to the size 

 of the fish or entirely absent ; by the development of tactile 



1 From Gunther's Fishes. 



Fig. 170. A deep-sea fish 1 



