XXIV EEPORT OF THE COMMISSIONER OF FISHEEIES 



The total economic loss due to this factor is incalculable, and much 

 efi'ort has been expended in an attempt to control the mosquitoes, 

 which are responsible for the spread of the disease. 



For a number of years the bureau has been conductin<i: experi- 

 ments in the use of certain small fishes {Gamhusia affinis) in the 

 control of mosquito production Avith marked success. At the pres- 

 ent time this method is used extensively and is considered to be the 

 best under a variety of circumstances. During; the past year special 

 attention was given to the propagation of these fishes on large tracts 

 of land that Avere to be flooded. By properly stocking the small, 

 natural bodies of Avater found in the areas to be flooded it is ex- 

 pected that efficient control may be secured from the very first in the 

 artificially formed lakes. A paper giving the results of this Avork 

 has been prepared. 



Experiments on the effects of variations in temperature and rain- 

 fall on the efficiency of Gambusia in controlling mosquito produc- 

 tion Avere continued at Augusta, Ga. The season Avas unfavorable 

 on account of periods of heavy rainfall, Avhich caused flood conditions 

 to prevail. Some valuable information was secured, hoAvever, and a 

 comprehensive report has been prepared for publication. Arrange- 

 ments have been made to conduct similar experiments in the region 

 about GreenAvood, Miss., and a field laboratory has been established 

 at that place. 



This Avork has been carried on in cooperation Avith the United 

 States Public Health Service and the Board of Health of Augusta, 

 Ga. 



OCEANOGRAPHIC AND LIMNOLOGICAL INVESTIGATIONS 



In connection with the investigations into the cause of the marked 

 depletion of the oyster resources in Long Island Sound studies have 

 been made of certain conditions to be found there Avhich are inimical 

 to the growth and survival of the larval oysters. A considerable 

 increase in the acidity of the Avater was observed in the Ho'usatonic 

 KiA^er and in Bridgeport and Ncav Haven Harbors. Other oceano- 

 graphic observations Avere made in connection Avith the survey of the 

 oyster resources of Georgia and the study of the spawning and early 

 history of the cod. Serial temperatures were taken and horizontal 

 and vertical tows made along the coast of Maine, in Massachusetts 

 and Cape Cod Bays, and on Nantucket Shoals. Arrangements for 

 taking an extensive series of temperatures at a number of selected 

 lightships and lighthouses along the Atlantic coast haA^e been com- 

 pleted. Work on the preparation of the report on the oceanography 

 of Chesapeake Bay Avas continued, and it is expected that this Avill be 

 completed in the near futuie. 



Various studies pertaining to the physical and biological condi- 

 tions existing in certain fresh-Avater lakes in Wisconsin have been 

 continued. 



FOULING or ships' BOTTOMS 



An investigation of the nature and extent of the fouHng of ships' 

 bottoms was begun in 1922 in cooperation Avitli the Bureau of 

 Construction and Repair of the Navy Department. It Avas con- 

 tinued during the past year at NeAV York, Norfolk, Va., and Beau- 



