PREVENTION OF COSTIA NECATRIX IN SALMONOID FRY. 923 



These measures of precaution and a careful maintenance of cleanliness in 

 the hatching boxes, etc., as well as the sole use of live natural food, brought 

 about only the result that in the two boxes first installed the fry did not develop 

 the Costia until four or five days later than in the hatching house, and that the 

 infection did not spring up immediately in a violent form, but crept in upon 

 them slowly and insidiously. It may be concluded thence that after the clean- 

 ing and thorough disinfection of the pond, etc., the water was free from Costia, 

 but was reinfected by the nonsaturated ground of the banks, from cysts which 

 must have been carried into the water by the wind. But whence come these 

 cysts? The following explanation readily presents itself: 



The dirt from the rearing troughs (during the first years of my direction 

 there were eight of them at three different places, for the most part occupied 

 by two separate lots of fish), the excrements, debris of food, and ooze from the 

 algae and the grounds were washed down into the pond water; there formed 

 in the wintering ponds during eight to nine months at the places where the 

 water did not course so freely a thick layer of fat, black, ill-smelling ground 

 ooze, and the ponds could not be cleaned except by flushing them out, scrap- 

 ing, sweeping, and washing out the ground; all this carried off into the principal 

 pond. The latter can be emptied only down to about five-sixths of its contents, 

 and all the springs of the local systems flow into it, through it, and off by means 

 of one lock. From the principal spring, which is easily accessible to the village 

 of Studenec (three or four butchers, the cattle, etc.), much organic matter comes 

 into the pond; it continually receives manure from this source, and incidentally 

 from the well-frequented road during rainfall. Thus a rich bottom fauna and 

 very abundant vegetation develop. The latter must be taken out partially 

 several times a year and thoroughly once annually. Much ooze is naturally 

 taken out with the Chara fragilis, and everything taken out of the pond is 

 piled on the banks in heaps, where it remains sometimes for two entire years. 

 As long as the springs were full and there was a corresponding flow of water, 

 a total of 600 to 800 second-liters in the maximum and never less than 200 

 second-liters up to 1896, no bad effect was noticed on the fishes from the pollu- 

 tion of the ground and its oxidation. And, frankly speaking, I knew nothing, 

 as so many others, about the importance in fish rearing of ground culture and 

 ground sanitation. When the scarcity of water and lack of currents began to 

 be felt and had grown quite noticeable in 1904, and the well-known effects of 

 such conditions, among others the presence of Costia, appeared in the fish-cul- 

 tural work, I was forced to look for explanation and remedies. 



Conditions for the existence of Costia were rendered more and more natur- 

 ally favorable by the decrease of water supply in the summer of 1 905 , the winter 

 following, and later down to a very few liters, and by the fish-cultural opera- 

 tions; and the persistence of the infection was insured by the maintenance of 



