94 REPORT OF THE SECRETARY OF COMMERCE 



nutrition, which have been under way for several years with the 

 State of New York, Cornell University, and the Bureau, have been 

 continued. As a result of these investigations, improved trout diets 

 have been devised and numerous problems regarding the digestibility 

 of food materials have been solved that should aid in reducing cost 

 of hatchery operations throughout the country. Similar study of 

 hatchery and stocking problems have been undertaken on a coopera- 

 tive basis in California, concerned primarily with problerhs of man- 

 aging the supply of steelhead trout in coastal streams and of the 

 various trout species in the high mountain regions. 



Fish pathology. — Progress has been made during the year in the 

 study of fish diseases that annually take heavy toll of the fish in 

 hatcheries. Experiments on two of them, the so-called " ulcer dis- 

 ease " and " blue sac disease ", have been made in an effort to find 

 preventives or cures, and a clinic or disease service has been estab- 

 lished to aid fish culturists in their practical problems of disease 

 prevention. In this service prompt diagnosis of diseases is given by 

 mail when fishes are sent to the laboratory for examination. 



Stream surveys. — Utilizing funds provided by the Public Works, 

 stream surveys were conducted by 16 parties operating in forests 

 and parks in various parts of the country. The primary purpose of 

 the surveys was to provide an inventory of conditions that affect 

 the fish population in each lake and stream. With this information 

 at hand, it has been possible to determine to what species of fish 

 each body of water is best adapted and the number it can support 

 most advantageously. One-sixth of the waters of our national for- 

 ests have been surveyed during the past year, with the result that 

 many miles of water formerly stocked have been shown to be worth- 

 less and in some localities suitable waters are neglected. Greater 

 economy and efficiency can, therefore, be introduced into the stocking 

 program. 



In connection with the stream surveys, extensive work in stream 

 improvement was carried out in the national forests for the pur- 

 pose of increasing the carrying capacity and food production in 

 streams. Since there are few reliable data on which to base an 

 estimate of the true value of stream improvement, the work was 

 primarily experimental, and its real result will be apparent only 

 after several years. 



Pollution of waters. — One of the most serious limitations on the 

 maintenance of abundant stocks of food and game fishes in interior 

 waters and the chief hindrance in stocking these waters with addi- 

 tional supplies is pollution from domestic and industrial sources. The 

 destruction of fish life by polluting substances, already acute in many 

 localities, is rapidly growing throughout the mor,e densely settled 

 and industrialized sections of the country. 



Without authority, until the passage of the " Coordination Act " 

 March 10, 1934, the Bureau has made during the past year, with an 

 allotment of funds from the Public Works Administration, a very 

 promising start on an investigation of pollution problems related to 

 the conservation of aquatic life. The standards of water purities for 

 the protection of aquatic life differ from those applying to indus- 

 trial uses of water or for the protection of public health, and are to 

 a certain degree more exacting. 



