XII KEPORT OF THE COMMLSSIONER OF FISHERIES 



Service and the Board of Health of Augusta, Ga. Special attention 

 ■was given to the effects upon mosquito control of seasonal varia- 

 tions in temperature and rainfall. It has been shown that the top 

 minnow (Ganil)usia) is not uniformly effective as an agent for 

 mos(juito control. Under certain conditions it has been found to 

 give an almost perfect control of mosquito production, and it is 

 of prime importance to discover just what factors contribute to 

 this efficiency. It is dificult to estimate the importance of mosquito 

 control in the Southern States where malaria is prevalent and 

 causes much distress and inefficiency. An adequate control of mos- 

 quito production is a pressing need of sanitarians, and it is felt 

 that the work do"ne to develop the use of fish for this purpose is 

 of great importance. 



In addition to a study of the effects of variations in temperature 

 and rainfall, experiments have been conducted to determine the 

 relative effectiveness of Gambusia in waters containing growths of 

 A'arious aquatic plants. Similar experiments have been condu(;ted 

 in previous years, and it is expected that this work, when summar- 

 ized and analyzed, will do much toward establishing the value of the 

 top minnow as an agent for mosquito control under a variety of 

 conditions. 



FOULING or ships' BOTTOMS 



The investigation of the fouling of ships' bottoms, begun in Sep- 

 tember, 1922, in cooperation with the Bureau of Construction and 

 Repair of the Navy Department, has been continued, and observa- 

 tions made during the winter of 1922-23 were further confirmed. 

 I)uring the year examinations were made of over 100 ships, rep- 

 resenting approximately equal numbers of naval and commercial 

 vessels. It has been shown that fouling occurs almost entirely while 

 the vessels are in port, those which are seldom in port and which 

 spend considerable time at sea accumulating little fouling. Fouling 

 is caused primarily by barnacles, with hydroids, alga^, bryozoa, and 

 jiscidians next in the order of their relative importance. It has been 

 ^hown that light bears an important relation to the extent of fouling, 

 and experiments were conducted to determine the reactions to light 

 of the organisms commonly involved. These show that for certain 

 species of barnacles, bryozoa, and tunicates the larvae have a tend- 

 ency to avoid the source of light at the time of attachment. 



Collections of adult barnacles and of data regarding breeding 

 habits at various stations on the Atlantic coast and at different 

 periods throughout the year have been made to determine the sea- 

 sonal occurrence and distribution of the "infective stages" of the 

 barnacles. Studies of the life histories and of the factors determin- 

 ing distribution of several species of barnacles have also been made. 



INVESTIGATIONS IN EL SALVADOR 



At the request of the Minister of Agriculture and Education of 

 El Salvador, Central America, the ichthyologist, accompanied by a 

 representative of the division of fish culture, undertook a study of 

 the fish and fisheries of that country. The survey was made for the 



