BUREAU OF FISHERIES XXV 



being conducted in the Upper Mississippi Wild Life and Fish Refuge, 

 Avhere it has been demonstrated that the sk)ughs and ponds adjacent 

 to the Mississippi River can be used to produce bhick bass in con- 

 siderable quantities. 



Trout-cultural investigations were continued at the Pittsford (Vt.) 

 experimental hatchery Avhere feeding experiments have been under 

 way for several years. Additional foods have been tested, the most 

 striking results being obtained from the use of dried salmon eggs. 

 Commercial fish meals were also employed and superior rations have 

 been devised at material savings in cost over foods generally used in 

 hatcheries. Breeding experiments to develop brood stocks of superior 

 quality, which were begun several years ago, have been continued, 

 and experiments in stocking local w- aters with black-spotted trout and 

 Montana graylings have been notably successful. At this hatchery 

 the diseases of trout were also studied. 



An investigation which promises to become of considerable impor- 

 tance has been undertaken on the diseases of the sea herring of the 

 coast of Maine. 



An important part of the bureau's pathological studies has been 

 conducted in numerous hatcheries throughout the eastern section of 

 the United States. 



SHELLFISH INVESTIGATIONS 



The bureau's investigations of shellfish, aside from the razor-clam 

 census referred to in connection with Alaska fishery investigations, 

 include two distinct and totally imrelated projects. One deals with 

 the 03"ster fishery and the cultivation of oysters on the eastern and 

 western coasts of the United States as well as the Gulf area, and the 

 other deals with the fresh-water mussels of the Mississippi River and 

 the attendant problems of pollution. 



Oyster investigations were conducted during the fiscal year 1931 in 

 Southern New^ England, Chesapeake Bay, in various South Atlantic 

 States, and on the Pacific coast. A study of causes of mortality of 

 oysters in the lower Chesapeake Bay was finished and a preliminary 

 report issued. The results' of this w-ork, which began in May, 1930, 

 and which was carried out in cooperation with the Fisheries Commis- 

 sion of Virginia, show that the mortality of oysters in 1929-30 was 

 caused by the concurrence of a number of unfavorable factors, 

 namely, low oxygen tension in the w^ater during the fall and winter 

 of 1929, planting oysters on soft bottoms, and overcrowded conditions 

 in some of the planted areas. The report stresses the necessity of 

 employment of better oyster-cultural methods, and outlines the gen- 

 eral policy for the development and maintenance of public reefs in 

 the State of Virginia. 



The main difficulty in the South Atlantic States is the overcrowd- 

 ing of oysters by a new crop of seed oysters that set on the old ones. 

 It is planned to develop a method of control of setting whereby the 

 crowded conditions on the reefs can be overcome. In several localities 

 substantial areas of oyster bottoms were set aside for experimental 

 purposes. 



In New York and Connecticut the work on the method of control 

 of starfishes and other enemies of oysters has been continued. 



