PREVENTION OF COSTIA NECATRIX IN SALMONOID FRY. 927 



EXPERIMENTS IN THE POND. 



It was not possible to arrange a waterfall there. I placed two barrels con- 

 taining 200 liters, so that the water flowed, as in the hatchery house, through 

 longer or shorter rubber tubes, according to necessity, and in slender jets into 

 all the hatchery boxes. The board covering of the cut-off part of the pond had 

 been removed in the preceding autumn and had not been renewed. The maxi- 

 mum of the pressure was 118 centimeters in both barrels, the minimum 33 

 centimeters. The filling of each of the barrels took place at least twice daily, 

 later even as often as five times. During the first week the water had to be led 

 up from the pond over a small scaffolding, as the spring was still too weak, but 

 after some rainfall the water could be pumped straight from the pond. 



On March 27 two boxes with 5. foniinalis were set up. On April 4 Costia 

 was noticed among them in spite of the jet of water from the barrels. The 

 daily aeration of the water for i >< hours to 2 hours was of too short duration 

 and too little effective with the pressure obtaining. The outflow pipe of the 

 barrel and the small opening of the nozzle were frequently clogged by things 

 carried in by the wind and taken up by the pump. 



There were seven boxes in all and in each of these the fry received a salt bath 

 of 2 per cent for thirty minutes every other day. To all appearances the aeration 

 and the streaming of the water from the barrels did not remain without effect. 

 The boxes could be thoroughly cleaned during the whirling of the water, and it 

 could not be denied that the fishes grew more lively in the currents, darting 

 through the whirls after the food without paying any attention to the fact that 

 the jet of water pressed them downward; and, the most important of all, losses 

 were not so frequent as heretofore and amounted (by estimate) to not over one- 

 quarter in the maximum, and in a lot of 5. irideus it was very small, in fact 

 inconsiderable. 



This lot came from large, beautifully colored parents. I had, however, done 

 a foolish thing with the eggs. Since it is very difficult and takes a great deal of 

 time to place the eggs regularly on the tiles so that they will not touch each 

 other, I had ordered flat, round depressions made in regular rows in two zinc 

 sheets in order to facilitate the work. The placing of the eggs was effected 

 beautifully, but think of my horror to see, after opening the breeding boxes, 

 instead of the hoped-for i ,900 or 2,000 fry, only 378, although these were almost 

 all large and fine. Ooze had settled in the depressions with the eggs and filled 

 the spaces between them. 



On April 14 these fry were put in the pond and were cared for more than the 

 others in regard to food and aeration. Up to May i the losses amounted to 25 

 fishes; up to June 3 there were only three more. After June 1 1 there remained 

 only three boxes to be taken care of, and the above mentioned irideus were 



