70 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



This brings us at once to a consideration of the life-histories of the fishes them- 

 selves. We must determine under what conditions each of the various species of food- 

 fishes thrives in its natural state; we must determine the temperature and chemical 

 character of the water in which it is found, the volume or size of the stream or lake, 

 the character of the shores and bottom and the surrounding' country; we must also 

 determine what other species of fishes are found associated with it, their abundance 

 and habits; and the same regarding any and all other species of animals and plants 

 found in or about the fish's home. And then, after the determination of the facts 

 regarding the fish's environment, a second and vastly more difficult series of investi- 

 gations must be taken up, namely, the hearing of each of these tacts upon the life of 

 the tish. 



The fact is one thing; its value as a factor in the lite of the fish is a very different 

 thing. I find a certain species of fish in a stream which has a mud bottom and whose 

 water has a temperature of 60 degrees at noon during dog-days. Am I justified in 

 concluding that a mud bottom and water of 00 degrees temperature are favorable con- 

 ditions for the growth of that species of fish? Not by any means. In the mountains 

 of East Tennessee last week I saw cornfields on mountain slopes too steep for an ordi- 

 nary man to climb with any comfort, but 1 must not infer that steep hillsides are a 

 favorable condition for the growth of corn. 



One of the divisions of the Fish Commission, as now organized, is the division of 

 fish-culture. This division has to do with the breeding, hatching, and rearing of 

 various species of food-fishes and the stocking and restocking of different streams 

 and lakes of the country. 



To do this work intelligently it must necessarily be based upon a knowledge of 

 the natural conditions under which each species thrives, which of the factors in its 

 environment are essential, which only desirable, which negative, and which detri- 

 mental to the best life and growth of the fish. And when it comes to stocking, the 

 division must know the conditions which obtain in every stream and lake which it is 

 proposed to stock. 



Another branch of the Commission — the division of scientific inquiry — in addi- 

 tion to its many and important lines of investigation regarding the marine fishes and 

 fisheries, has endeavored not to neglect the fresh-water species. It has undertaken 

 to carry on such a series of comprehensive and exhaustive investigations as will, in 

 time, result in a pretty thorough understanding of all the conditions under which our 

 various food-fishes thrive best and the particular significance of each factor in this 

 best environment. 



We have undertaken such a study of the streams and lakes as will enable us to 

 know the peculiar conditions which exist in each important hydrographic basin in the 

 United States. 



This, of course, means careful observation and study of all the physical, chemical, 

 and biological features of each stream, for these are the conditions, forces, or elements 

 which together constitute the tish environment, and which determine the presence, 

 abundance, distribution, and condition of the various kinds of fishes found in each 

 particular stream or lake. 



Most of the work which has been done so far has been in the line of deter- 

 mining the factors in each environment, rather than guessing what the factors mean. 

 Heretofore great harm has been done by guessing at the facts and also guessing at 



