92 REPORT OF THE SECRETARY OP COMMERCE 



Under such a program fish will be planted where they will do the 

 most good and the mistakes inherent in the old haphazard system of 

 planting avoided. 



The stream-improvement work has been undertaken in coopera- 

 tion with the Forest Service. Under this arrangement the Bureau, 

 has planned and supervised the work which has been done with labor 

 furnished by the Civilian Conservation Corps. 



Investigations of means of improving hatchery practices and pro- 

 viding better control of fish diseases have been continued. Breeding 

 experiments with brook trout have been so successful in developing 

 superior strains of fish that the work has been extended to include 

 rainbow and brown trout. 



SHELLFISHERIES IN\^STIGATION 



The various problems of the oyster industry were studied in 

 Massachusetts, Connecticut, North Carolina, Florida, Louisiana, and 

 Washington. In cooperation with the Connecticut Shellfisheries 

 Commission, the Bureau continued observations on the growth, fat- 

 tening, and seasonal changes in the nutritive value of oysters from 

 the experimental farm near Milford, Conn. In New Haven Harbor, 

 where dredging operations in the channel threatened the oyster bot- 

 toms, a series of analyses of the water was made for the State au- 

 thorities and the amount of silt in the water and its rate of settling 

 were determined. 



In North Carolina the Bureau's experts worked out the plans of 

 restocking the depleted oyster bottoms and supervised planting op- 

 erations carried out by the State. 



The development of new oil fields in the inshore waters of the 

 Gulf of Mexico creates a new difficulty to the oyster industry. A 

 question has arisen as to what extent the oil in the sea water may 

 affect the oyster bottoms in the vicinity of the oil wells. This diffi- 

 cult problem has been studied in the field and experimentally under 

 controlled laboratory conditions at Beaufort, N. C, Woods Hole, 

 Mass., and Washington, D. C. It has been found that the presence 

 of crude oil in the Avater decreases the rate of feeding of the oyster 

 and adversely affects the propagation of diatoms which are used by 

 the oyster as food. 



A disease of oysters caused by a protozoan parasite, which may 

 have been responsible for the mortality of oysters observed in 

 previous years in certain sections of the coast, was studied at Beau- 

 fort. The investigation has not been completed, but several phases 

 of the life history of the microorganism have been revealed. 



On the Pacific coast studies of the cycles of setting of the oyster 

 larvae proved of great value to the oystermen who arranged their 

 planting operations in accordance with the information and advice 

 supplied by the Bureau's laboratory at Olympia, Wash. 



POLLUTION STUDIES 



New methods for the biological assay of polluted waters have been 

 developed and put into practical operation at the field stations at 

 Columbia, Mo., Fort Worth, Tex., and aboard the floating laboratorv.. 



