FISHES 143 



the stomach and partly digested, whereas the tail 

 still projected from the mouth. 



Some species, particularly those that strain their 

 food from the water in the form of microscopic or- 

 ganisms, appear to feed constantly, for they do not 

 acquire their food in large quantities at one time. 

 Others, as has been already shown, gorge themselves 

 at one gulp and then, of course, cease feeding until 

 their meal is digested and hunger prompts a re- 

 newed search for food. The goose-fish, which feeds on 

 almost any kind of animal life of suitable size, fre- 

 quently contains within its stomach a quantity of 

 food equal to half its own weight. 



It has already been stated that the majority of 

 our fishes live wholly or partly on an animal diet. 

 Many animals eaten by fish in turn feed upon other 

 animal life. The original source of food of all ani- 

 mals consists of plants, and therefore, in the final 

 analysis, all fish depend upon the plant kingdom for 

 food. The close relationship, that is, the dependence 

 of one form of animal life upon another and their 

 final dependence upon plant life, has generally not 

 been given sufficient study. The decline in the abun- 

 dance, or the total disappearance, of certain fishes 

 from various waters has been charged to over-fishing, 

 or to the presence of introduced species, whereas in 

 reality the main cause of the decline was a break 

 somewhere in the chain of food supply. Pollutions 

 incident to an ever-increasing population and con- 

 sequent industrial development without doubt con- 

 stitute the chief cause for the scarcity of certain 

 fish foods, resulting in a decline in previously abun- 



