PREVENTION OF COSTIA NECATRIX IN SALMONOID FRY. 92 1 



contaminated by dust, etc. Doctor Robida took advantage of the vicinity of 

 the tank to supply with water therefrom two small aquaria in his room (1905). 

 From the main pipe, made of lead, the water passed into the aquaria through 

 slender rubber tubes (3 millimeters in diameter at the outlet) with brass end 

 pieces (about i millimeter at the opening), under pressure of about half an 

 atmosphere. One of the aquaria consisted entirely of glass and had a bottom 

 area of 35 by 25 and a height of 22 centimeters, while the other was somewhat 

 larger and had a lead bottom and frame, with walls of glass. In the bottom of 

 each was a layer of 5 to 6 centimeters of fine, white, well washed, calcareous 

 sand, and a few shoots of water cress were planted in it. The water, falling in 

 a slender jet, boiled up actively and sent out small bubbles in every direction, 

 so that even in the corners they could be seen dancing in the water. In the 

 first aquarium were placed more than 300 young Sahelinus jontinalis old enough 

 to feed, while in the larger one were placed Salmo fario and irideus, also a few 

 jontinalis, in all some 500 fry. More than any other fry these were fed with 

 crustaceans exclusively, which were greedily devoured, especially by the Amer- 

 ican species, which fed until the body swelled quite out of shape and looked as 

 if it would burst. The excrements were removed daily by means of a small 

 suction tube, while once each week the aquarium was thoroughly cleaned, the 

 sand washed, etc., the fishes being placed in other quarters during this pro- 

 ceeding. Costia had in the meanwhile appeared in the hatchery as in the 

 preceding years, but there was no trace of the disease in the aquaria. 



Ten diseased Sahelinus fontinalis were now put into the smaller aquarium. 

 The infection had not as yet shown its full effect on them and Costia had estab- 

 lished itself microscopically on other fishes looking like these. The diseased 

 fishes differed from the fat, healthy ones, not only by the thinness of body but 

 also by the coloring, which was more or less of a dark blackish blue hue, with a 

 faint, almost invisible shading as compared to the light-colored and white 

 markings of the healthy individuals, and the difference was apparent to the 

 casual observer. The diseased fishes continued to live, seeking the bottom in 

 the quietest places and rarely moving about, and looked at the last like a thin 

 blackish thread with a thick knot. All died within 6 to 9 days after the fishes 

 of the same lot and of the same appearance left in the hatchery. Expecta- 

 tion as to the results of this experiment was naturally great, but no effect was 

 produced on the fishes in the aquarium. 



A second experiment in the second aquarium gave the same result, and 

 several more were made in each aquarium. Doctor Robida attempted to con- 

 vey the infection by other means, i. e., by the infiltration of infected water and 

 by the direct introduction of living Costia, but with no result. He changed the 

 food freely, giving the fishes, when they had grown larger, grated meat from 



B. B. F. 190S— Pt 2—16 



