PREVENTION OF COSTIA NECATRIX IN SALMONOID FRY. 925 



to the Wocheiner Lake, a journey from 5.30 a. m. until i p. m., without incur- 

 ring any loss; the fish were from 5 to 7 centimeters in length. 



I could not detect that the salt water did any harm to the fishes. The 

 water was of course aerated incessantly by taking it up in a 2-liter vessel and 

 pouring it back from a height of 50 to 70 centimeters. Only the Salmo fario 

 remained at the bottom during this proceeding; the irideus and the jontinalis 

 had to be kept out of the way with a gauze hand net. 



Doctor Robida did not take any part in my experiments in 1906 and 1907, 

 and left Studenec last year. 



THE SEASON OF 1908. 



The drying up of the springs, which was no longer doubtful, in addition 

 to the spreading of the Costia, decided those in authority to abandon the locality 

 near Studenec. But my desire and hope that my fish-cultural difficulties would 

 end with the year 1907 were not fulfilled, as the spawning season of the sal- 

 monoids came round before measures for abandoning the locality could be taken. 



Since I could command my time, I wished to make use of my knowledge 

 of the effect which the introduction of atmospheric air had upon Costia. I 

 sought, first, suitable cyHnders, similar to those of the Hydrobion; air was 

 pumped into these and was to rise gradually from the bottom of the fish troughs 

 in small bubbles to the surface. Two attempts to obtain the clay cylinders 

 met with failure. 



Salt baths are good, and capable of saving the fry from entire or enormous 

 losses; but they can not be lastingly effective if the water is continually 

 infected anew, and they must, consequently, be repeated; and even while apply- 

 ing them every forty-eight hours I had to register losses which amounted in 

 time in the most favorable cases to one-fourth of the fishes placed in the basin. 

 They also take much time, for a man can accomplish at the same time the 

 necessary aeration of the water in but two or three hatching boxes at the most ; 

 ten boxes would thus demand four to five hours. 



EXPERIMENTS IN THE HATCHING HOUSE. 



The distributing trough in the hatching house stands some 48 centimeters 

 above the ground and is 22 centimeters deep. I placed the hatching box on the 

 floor and obtained thus a fall of 33 centimeters. A siphon having 8 millimeters 

 interior diameter gives, by exact measurements, 4.2 liters per minute ; the capacity 

 of one box is 2,514 liters, and the water is changed therein in 5.98 (6) minutes 

 with one siphon and in three minutes with two. I placed above the hatching 

 box a basin 75 centimeters interior depth, containing 250 liters of water. The 

 water flowed therefrom into the hatching box through a flexible rubber tube i 

 centimeter interior diameter and with a conical nozzle of zinc with an opening of 



