CHAPTER III 



DISTRIBUTION AND LOCATION 



Fresh-water fishes and marine fishes. Physostomous fishes originally be 

 longing to fresh water, and Acanthopterygians which have returned thither from 

 the sea. Fresh-water fish-fauna of the great continents. Natural homes and 

 habits in littoral zone. Tropical fishes. Arctic and Antarctic fishes. America 

 and Europe. North Pacific. South Africa. India. New Zealand and Australia. 

 Pelagic fishes. Abyssal fishes. 



IN considering the waters of the earth as the habitat of 

 fishes, the first distinction that we naturally make is be- 

 tween the fresh waters and the sea. The conditions in 

 the former are necessarily different from those in the latter, 

 although there are regions of transition between the two. In 

 the rivers space is more limited, light is abundant, the vege- 

 tation and animal life are quite different from those in the sea, 

 but the chief difference is the absence of salt from the water. 

 In some cases communication with the sea is difficult or impos- 

 sible, but even where it exists many species do not migrate and 

 cannot live in salt water. Temperature limits the range of 

 some species, those which are natives of the tropics could not 

 survive in colder regions, but the fact that fish of various species 

 thrive and multiply when introduced to distant regions of similar 

 climate where they do not naturally occur, shows that their 

 natural range is determined not merely by suitable conditions, 

 but by physical barriers to dispersal. As we have seen in con- 

 sidering the evolution of fishes, the Elasmobranchs are almost 

 entirely marine, only a few of the flattened forms, belonging to 

 the Sub-Order Batoidei, entering large rivers in the tropics, 

 and a few becoming land-locked : Indian species of saw-fishes, 

 Pristis, thus enter rivers, and one in the Gulf of Mexico ascends 

 the lower Mississippi. Some species of Trygon or sting-rays 

 are confined to fresh water in the northern part of South 

 America. Nearly all the surviving primitive bony fishes, on 



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