TROUT WATERS AND CARP WATERS 



ologists call this " respiratory combustion ", and it is 

 a good name because, like ordinary combustion, the 

 action consists in an expenditure of chemical energy 

 in which oxygen plays the principal part. One of its 

 main ends is a setting free of carbon-dioxide. 



Every act of combustion, every oxidization, is accom- 

 panied by the production of heat, though the degree 

 varies. This is sometimes immediately counteracted, 

 so that it is hardly noticeable, sometimes set free, at 

 least in part, and there are evident traces of it. The 

 caloric energy thus engendered is essential to the 

 maintenance of life, The other vital activities depend 

 upon it, and can only manifest themselves, as it were, 

 on its terms. If it goes beyond the limits of " organic 

 well-being ", or if it falls below them, life hesitates 

 and there is a breakdown. Among fishes, the trout 

 and similar species occupy a privileged position. 

 Endowed with a particular intensity of respiratory 

 oxidation, they can resist low temperatures almost 

 to freezing point, continue living in waters affected 

 by such temperatures, and carry on the majority of 

 their vital activities in them. In this fact, probably, 

 we find the reason for the special characteristics which 

 fit them among fresh-water species for their peculiar 

 mode of life. 



They have a high coefficient of respiration, which 

 means that, in a given time, a definite weight of their 

 flesh absorbs a greater proportion of oxygen than in 

 the case of fishes less well equipped. Consequently, 

 the result of the intensity of their oxidizing processes 

 being the production of a greater caloric energy, their 

 organism continues to be able to work, despite the low 

 temperature of the environment. In the middle of 

 winter, in mountain streams whose water is only a 

 few degrees above freezing point, the trout come and 

 go and breed, their eggs hatch, and their fry develop 

 without any difficulty. 



The carp are in a very different position. Their 

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