563 



these problems? These are questions which continually occur 

 to one familiar with this locality, observant of the operations 

 of fishermen, and cognizant of some of the seasonal flux of 

 life and matter in this water world of which fish are but a 

 part. 



The plankton is an integral part of the chain of food rela- 

 tions which extends from the water, with the gases, salts, and 

 products of decay dissolved therein, on the one hand, to the 

 fish and other vertebrates of commercial importance upon the 

 other hand. The water, the carbon dioxid dissolved therein, 

 the nitrogenous matters, and various salts in solution are util- 

 ized either by the grosser aquatic vegetation or by the micro- 

 scopic phytoplankton. In the former case the growing plants 

 are rarely utilized directly as food by any aquatic animals. A 

 possible exception to this statement is found in the case of the 

 turtles. Fishermen are accustomed to feed these animals, 

 when penned up for the market, upon "moss" or CeratophyJlum, 

 though it may be that the insect larvae and mollusks found in 

 the vegetation constitute the more important elements of 

 the food. It is only when this growth of vegetation decays 

 that it releases into the water the elements which conduce to 

 its fertility. 



The phytoplankton, on the other hand, multiplies very rap- 

 idly and is immediately available for the support of the micro- 

 scopic animals of the zooplankton, and this, and to some ex- 

 tent also the phytoplankton itself, is the immediate food of 

 most young fish uj)on hatching and the customary food of some 

 adult fishes, — such as Fobjodofi (Forbes, '88, and Kofoid, '99) and 

 many minnows, — of the bivalve mollusks, and of many other or- 

 ganisms of sessile habit. The plankton is thus the prime source 

 of food of fishes and of many other organisms utilized by fish 

 as food. The chain of food relations, for example, between 

 the food elements of the water and the black bass is in the 

 main a short one, with the plankton as the principal link. Pro- 

 fessor Forbes ('80) has shown that 86 per cent, of the food of 

 the game fish consists of other fishes, principally Dorosoma with 



