Stream Pollution 17 



with. Migrating fish, like shad or salmon, that seek definite parts of 

 the stream system for spawning, are compelled, in the absence of 

 satisfactory locations, to spawn on polluted areas, and the eggs have 

 little chance to develop properly. As the organism is exceedingly 

 susceptible in this stage of its existence, conditions which could be 

 endured by the adult fish will often prove fatal to the eggs. These 

 conditions prevent the species from holding its own in the face of the 

 demands upon the supply that are made by the fishermen. 



Still another feature demands consideration in this connection. 

 The state is breeding annually large quantities of young fish at 

 considerable expense. It takes at the appropriate season the eggs of 

 a given species, places them in a hatchery under proper conditions 

 of development, and, after having protected them through the period 

 of growth within the egg and perhaps, also, after having protected 

 and fed them through the earlier stages of existence, it has a mass 

 of fry or fingerlings to plant out for the rehabilitation of the stream. 

 These stages are not so sensitive as the tgg stage, for the fish with 

 every period of time that elapses from the start of its development 

 becomes more and more immune to the dangers of existence; yet 

 even in these free-swimming young stages, the fry and fingerlings 

 are much more delicate than the adult fish and will succumb to 

 conditions that would merely drive away the adult rather than 

 destroy them. It is hardly a profitable business for the state to raise 

 at such a considerable expense quantities of young fish in order to 

 plant them out in waters in which the chances of existence are 

 unfavorable. 



To summarize this phase of our study: 



The pollution of the water, especially by industrial wastes, results 

 first, in the geath of the adults ; or second, in driving them away 

 from polluted ?ireas. It makes the territory unfit for natural repro- 

 duction and destroys the eggs of the fish, thus interfering with the 

 means" for the preservation of the species. Finally, it brings to 

 naught the efforts of the state for rehabilitating the supply of fish, 

 since the young fish which are planted maintain a limited and 

 precarious existence in polluted areas, if indeed they are not de- 

 stroyed by the unfavorable environment. 



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