20 U. S. BUREAU OF FISHERIES. 



by students from the university. The aquatic plants, the plankton, 

 bottom fauna, and mussels of Green Lake were studied during the 

 past year, with reference to quantity and distribution, and a report 

 onithe aquatic plants has been completed and will appear in Volume 

 XXI of the Transactions of the Wisconsin Academy of Sciences. 

 Arts, and Letters. Arrangements have been made for the continu- 

 ance of these investigations during the fiscal year 1924. 



FOULING OF ships' BOTTOMS. 



In September, 1022. in cooperation with the Xavy Department, the 

 bureau began an investigation of the marine growths on the bottoms 

 of ships to determine, if possible, the conditions governing the 

 amount and character of such growths and the possible seasonal and 

 regional factors affecting them. The work was undertaken with a 

 view of securing further data on the problems of preventing the 

 attachment of the fouling organisms to ships' bottoms, as well as to 

 determine the proper docking intervals for ships in various kinds of 

 service. J. Paul Visscher, of Johns Hopkins University, was placed 

 in charge of the work. Through the Navy Department he has been 

 kept in touch with the docking of vessels in the navy yards of the 

 Atlantic coast and has made examinations of more than TO vessels 

 in dry dock. 



While the results so far obtained are not entirely conclusive, suffi- 

 cient data have been collected to indicate that the color of the paint 

 used is an important factor in determining the extent of fouling. In 

 the tests made with submerged plates painted, respectively, white, 

 black, yellow, red, green, and blue, it was found that there was much 

 more fouling on the dark plates than on those of lighter colors. 

 These results apparently are explained by the fact that at the time 

 of attachment of the larvae to the plates the organisms are negatively 

 phototropic; that is, they tend to go away from the source of light. 

 It would seem, therefore, tliat there is an important and specific rela- 

 tion between light and the nature and extent of the fouling of ships' 

 bottoms. 



The investigation has also indicated rather conclusively that foul- 

 ing in the North Atlantic waters is caused, in the order of their im- 

 portance, by barnacles, hydroids, algae, brj^ozoa, ascidians, and by 

 numerous other growths of much less importance, and that most of 

 the organisms attach while the ships are in harbor. It has been 

 shown that vessels in commission, which never stay more than six 

 or seven days in any port and travel between ports a considerable 

 distance apart, do not foul seriously, at least during the period from 

 August to March in the North Atlantic Ocean. On the other hand, 

 it is found that vessels that lie at anchor continuously in any one 

 port for the five or six winter months become heavily coated with 

 hydroids but not with barnacles. 



INVESTIGATIONS PERTAINING TO FISH-CULTURAL OPERATIONS. 

 PATHOLOGY OF FISHES. 



Studies have been continued by Dr. H. S. Davis, pathologist, on 

 Octomitvs salmonis, an intestinal parasite of trout. In the course 

 of these investigations visits were made to a number of hatcheries 



