RADICAL PREVENTION OF COSTIA NECATRIX IN 

 SALMONOID FRY. 



By JOHANN FRANKS, 

 Director of the Fish-Culture Establishment at Studenec and Secretary of tlie Fishery Committee 



for tlie District of Krain. 



Jit 



[Translated from the German.] 

 CHARACTERISTICS OF THE DISEASE. 



I insist upon the limitation to " salmonoid fry," because I have not directly 

 observed Costia, nor have I seen the characteristic exterior appearances of 

 costiasis, on any adult fish with one exception. I saw four years ago in June, 

 in the Stara Voda, in a broad place in the stream where the current was very 

 slow, a pike some 23 centimeters in length with a whitish covering on the 

 skin resembling a veil, very like figures 12 and 13 in Dr. Bruno Hofer's 

 "Fischkrankheiten," in which work appears a full description of this disease." 



The place where my observations were made was the fish-culture establish- 

 ment at Laibach, Austria. 



The appearance of Costia was noticed among the fry some five to ten 

 days after they had begun to feed, i. e., after the resorption of the sac — never 

 before this period — and equally whether the fry began to feed early or late, 

 among the early feeding Salvelinus fontinalis and alike the late Salmo irideus. 

 About the middle of June, sometimes ten days earlier, all trace of Costia dis- 

 appeared as mysteriously as it had come. I have no reliable criterion as to 

 whether the fish became immune against costiasis in June or whether Costia 

 in the form of a flagellate is seasonal, but I suppose the latter to be the case, 

 since the signs of disease disappear at the same time among the younger and 

 older fry. 



No difference could be found in the susceptibility of the young fishes; the 

 fry of the three species regularly cultivated — Salvelinus fontinalis, Salmo fario, 

 and Salmo irideus, obtained from brood fishes of the establishment (among 

 which may be included the 100 kilograms of Salvelinus fontinalis and Salmo 



o Hofer, B.; Handbuch der Fischkrankheiten, p. 115-121. Munich, 1904. 



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