56 THE COMMERCIAL SEA FISHES OF 



animals. Fresh-water forms have been divided into the 

 river or fluviatile, and the lake or lacustrine classes. Cata- 

 dromous has been proposed for such species as eels, which 

 appear to pass a large portion of their lives in fresh waters, 

 but descend to the sea or littoral zone for the purpose of 

 breeding. Sea fishes have been subdivided into the pelagic, 

 or strictly marine forms ; the littoral, or coast species, and 

 the anadromous, which leave the sea for rivers, up which 

 they ascend in order to deposit their eggs in fresh waters, 

 where the young of some, as the salmon, are reared ; but 

 not so of others, as the shad. 



Pelagic fish, or the strictly marine forms, may be classed as 

 those which are commonly found at the surface ; mid-water 

 or median ; and such as reside in the depths of the ocean, 

 or the abyssal. The littoral zone is that portion of the sea 

 which extends from the shore to about 100 or 150 fathoms, 

 a depth at which the direct rays of the sun are limited a 

 region of light. Through this space almost any of the 

 littoral forms of fish may wander, and into this zone pelagic 

 forms may range in order to prey upon their neighbours, 

 deposit their ova, or having been driven in due to sickness. 

 In the littoral zone there are constant migrations, and fishes 

 from deeper localities press in after their prey. Professor 

 Agassiz considers, and with considerable grounds, that a 

 continental zone may be traced in the ocean, extending from 

 the littoral belt to 450 or 500 fathoms, which in some 

 localities is represented by a deep slope and where the 

 diminution of temperature is very rapid. The abyssal, 

 which I here consider commences at about 100 to 150 

 fathoms (thus excluding the continental zone), extends from 

 the littoral zone to the sea bottom to the greatest depths. 

 Here the temperature is low, darkness more or less com- 

 plete, while the forms of animal life appear to have remained 



