30 U. S. BUREAU OF FISHERIES 



observation may be noted in this connection — it was found that Mysis 

 relicta leaves the bottom of Trout Lake at night and migrates to the 

 surface. 



FOULING OF SHIPS' BOTTOMS 



The investigation of the fouling of ships' bottoms was continued 

 during 1925 both at New York and at Beaufort, N. C. This work 

 involved the examination of about 50 ships in dry dock and consider- 

 able experimental work at the Beaufort laboratory, and finally a 

 complete report covering all of the work has been submitted. 



On the basis of careful examination of 250 ships at the time of 

 dry-docking, it has been ascertained that fouling is caused by both 

 plant and animal growths, the latter being the more important where- 

 ever fouling was at all extensive. These were barnacles, hydroids, 

 algse, tunicates, br} r ozoa, mollusks, and protozoa, in the order of 

 frequency and usual abundance. 



It was soon noted that fouling organisms were almost exclusively 

 those forms commonly found on rocks near shore, especially in har- 

 bors, and it was found, furthermore, that fouling occurs almost 

 entirely while vessels are in port. Most ships were found to be mod- 

 erately fouled after 6 or 8 months from the date of previous dry- 

 docking, and it was shown that the time that elapses between dry- 

 dockings is of significance, for fouling increases with the interval of 

 time. However, fouling was least on ships that spent most of their 

 time cruising at sea. 



The data regarding relation of light to the amount and kind of 

 fouling, a relationship early noted on ships' bottoms, have been sup- 

 plemented by extensive experiments that demonstrate that light in 

 the field of green and blue-green has the maximum stimulating effi- 

 ciency for the cyprid larva? of several barnacles, and that at the time 

 of attachment these forms are negative to light. 



The relation of fouling to fresh water was also studied experiment- 

 ally, and it was demonstrated that fresh water kills, within 72 hours, 

 most of the organisms that cause fouling; but if calcareous growths 

 have already formed, such materials remain, and the resistance to 

 the movement of the ship is not materially reduced. 



A preliminary study of seasonal periodicity indicates that the 

 amount of fouling on a given ship can be predicted from a knowledge 

 of seasonal periodicity for the organisms in the ports visited. Indi- 

 cations of a selective process of attachment by barnacles have been 

 noted, indicating a relation between attachment and the nature of 

 the surface. 



INVESTIGATIONS PERTAINING TO FISH-CULTURAL OPERATIONS 

 PHYSIOLOGY AND NUTRITION OF FISHES 



Feeding experiments with fingerling trout were carried on during 

 the summer of 1925 at the Holden (Vt.) hatchery by M. C. James, 

 under the supervision of Dr. H. S. Davis. As previous experiments 

 at Manchester, Iowa, and White Sulphur Springs, W. Va., with rain- 

 bow-trout fingerlings gave such encouraging results, it was decided 

 to conduct similar experiments at a brook-trout station. For this 

 purpose, brook-trout fingerlings were divided into lots of 1,000 each 



