924 BULLETIN OF THE BUREAU OF FISHERIES. 



old and the establishment of new piles on the bank whence Costia cysts would 



be derived. I can not find any other explanation for the infection of the pond. 



Cooking salt was again our resort; by this means I carried through the 



critical period one-fourth of the fishes in the worst cases and three-fourths of 



them in the less severe. 



PRECAUTIONS APPLIED IN 1907. 



The same pond was again thoroughly cleaned and disinfected, then a part 

 was partitioned off in a shallower portion by means of a wall of clay. The 

 water for the fry flowed through a tube of rubber and lead through the dams 

 into the distributing trough and thence through lead siphons into the hatching 

 boxes. The covers for these were fitted better and more closely than in 1906, 

 and supplied with glass openings in order to give the fishes both light and sun 

 without having to take off the covers; the distributing trough was likewise 

 kept covered as much as possible and the cover was hfted only for the cleaning 

 of the boxes. The flow of water was increased by five, six, and eight times 

 the ordinary amount for the cleaning of the boxes, by which means the sediment 

 was whirled up, flooded through the closing screen, or deposited on the latter 

 to be swept off by means of a soft brush; the whirling up and flowing off of 

 the sediment was aided also by means of a feather. 



At the end of March, some ten days later, no trace of Costia was found in 

 two boxes of Salvelinus fontinalis; but only fourteen days later, on April 4, 

 I saw two fishes the color of which was not quite satisfactory. On April 5, two 

 fishes were dead and four or five had changed color. The naked eye and the 

 microscope both testified to the unwelcome truth — it was Costia again. March 

 was very dry and very windy during the latter days. I gave the fishes a salt 

 bath of some fifteen minutes duration on April 5 and 8. Then there was no 

 trace of the disease until the i8th, when I gave another salt bath. It again 

 appeared necessary to give the bath on the 20th, 24th, and 28th of April, on 

 the ist, 3d, 19th, 24th, and 28th of May, for twenty-five minutes, and, lastly, on 

 June 3 for thirty minutes, when the fishes were transferred to the rearing trough. 



The covering of the water was not entirely useless, the infection in the two 

 first boxes having had two long intervals, the first ten and the second twelve 

 days. The three lots nearest to the outflow needed the salt bath most frequently, 

 i. e., every other day without intermittence ; these were Salmo irideus of May 

 3 to June 13. The explanation of this fact is the following: The cover of the 

 trough had to be taken off every morning and every evening during cleaning 

 time, and this admitted the dust and the cysts, caught up by the wind, which 

 were brought by the current to the outflow in greater quantities than at the 

 place where the water flowed in. 



I carried through the critical stage about 4,000 Salvelinus fontinalis, which 

 were kept in three boxes, the last 1,400 being taken by myself on August 17 



