A STUDY ON TROUT AND YOUNG SALMON. 241 



Smitt, has with great hberality and kindness forwarded to me 

 for examination the specimens needed. 



Besides, the collections of salmon in the museeums of our 

 university, Bergen, Trondhjem and Tromsø, have been exa- 

 mined. 



The result of these investigations proves my working theory 

 to be correct, as I will endesavour to show. 



In the middle of June 1900 I cought in the mouth of the 

 river Gula some 150 emigrating young salmon (smolts). In 

 saved--off barrels or tubs they were kept about 1 week on board 

 of my sailingvessel. About 25 were kept in each tub (new 

 ones) the water being changed 4 — 5 times in the 24 hours. 



The vessel was towed to Trondhjem, and June 17, 150 

 smolts and about 20 trout of different stages were placed in 

 separate freshwatertanks. As the tanks, tubings and aquarea 

 for salt water were not yet in order, I had to keep my fishes 

 for nearly a fourthnight in freshwater. 



By transferring a few to seawater and letting them stay 

 there about a day, I satisfied myself that no trouble was likely 

 to arise from their passing from fresh to salt water. 



In the mean time a considerable mortahty occurred among 

 my young salmon. They would greedely eat ordinary rainworms 

 besides gammarids, which latter in large numbers were to be 

 had under de stones at lowtide. By and by however they were 

 attacked by the common freshwater fungus (saprolegnia) which 

 affected their gills, fins or those places of the body where scales 

 were lost. 



The fish once infected, this saprolegnia woud spread with 

 incredible rapidity. Thus I noted that the fungus in some cases 

 in about half a day would spread fj-om a small point, just di- 

 stinguisheable, to an area of about 2 square centimeters. Many 

 fishes succumbed during this period. 



On July 1 the aquaria for saltwater were ready for use. 

 I had then no more than 70 smolts left. These were in some 



Nyt Mag. f. Naturv XXXXII, III. 16 



