92 2 BULLETIN OF THE BUREAU OF FISHERIES. 



his own table, even chopped Uver, thinking that in water so well aerated even 

 such food could do them no harm." 



The abundant aeration of the water proved to be a radical prevention 

 against Costia, all the fish remaining alive and healthy, not one being lost. 

 When the action of the pump grew defective on account of scarcity of water, 

 Doctor Robida used a small motor operated by alcohol for the purpose of 

 obtaining a current in the aquaria. But the disadvantage increased and I put 

 the fishes, which were from 3 to 4 centimeters long, into a rearing trough (8 

 meters long, 0.55 meter wide, and 20 centimeters deep), merely giving them 

 three more salt baths, since this was the end of the critical period, in order to 

 be safe from the danger of Costia. 



I have never seen the white veil-like covering spreading over the skin, as 

 shown in figures 12 and 13 in Doctor Hofer's book, except on the pike already 

 mentioned ; never on the small fry. So long as I fought Costia with potassium 

 permanganate and not with cooking salt, as did Doctor Hofer, the fishes which 

 had withstood Costia had white fungus spots near the gill openings, and these 

 spots, in spite of the treatment with potassium permanganate, were in some 

 cases fatal. Since I have begun to use common salt, I have not noticed this 

 last phenomenon. I suppose that the fishes attacked by Costia are too small 

 and consequently too weak to endure this condition until the white spots 

 show on the skin, and die before this stage. 



EXPERIENCE OF THE SEASON OF 1906. 



It was impossible to arrange an aeration of the hatchery troughs by means 

 of water under pressure, on account of lack of fall in the supply. The only fall 

 periodically in operation was occupied by the already mentioned pump and not 

 available for hatchery purposes by reason of its location. Thus I could not put 

 into practice the new experience with aeration. 



Since Costia was again to be expected in the hatchery, however, I arranged 

 in a pond, which had not been used for fishes for four years and the water flow 

 of which was used only to supply two rearing troughs, a place in the open for 

 the hatching boxes. This small pond was repeatedly dry when the water was 

 low in the springs. The bottom was cleaned of all vegetation, raked and washed 

 out, highly saturated with potassium permanganate, and after this washed 

 out with salt. All the small fry able to feed and destined for rearing in the 

 establishment were brought to this pond. The water, as may be easily under- 

 stood, never grows muddy, has a constant temperature of 9.8° C, and produces 

 many green algae, which are very cumbersome when the ciurrents of the water 

 become slow with low water in the springs. 



o In my opinion such food can not be given long, never exclusively, and of the latter sort not 

 even to large fish. 



