American Fisheries Society. 85 



ap]3arently the creature that has been described under the name 

 of Gyrodactylus elegans. In hope of destroying tlie parasite, the 

 salt treatment was continued, but it was found at last that the 

 parasite could endure quite as much salt as the fish itself. Mr. 

 Seagle at Wytheville, has since discovered that this parasite is 

 readily destroyed, with entire safety to the fish by a bath consist- 

 ing of one part common cider vinegar, three parts water. The 

 mortality went on until the sufferers had shrunk from 39,000 

 July 1st to 10,000 in November, and the survivors were fish of 

 low vitality, of whom probably not one ever grew up. 



No unusual mortality occurring among the fishes of other 

 species reared alongside the lake trout, and under the same cir- 

 cumstances, it was a puzzling prol)leni why the Gyrodactylus had 

 made such an attack on the lake trout. The theory was at once 

 suggested that the parasites had been imported along with the 

 eggs, and the occurrence of a few specimens on other fishes in 

 neighboring troughs might easily have been accounted for on the 

 supposition of accidental transfer from trough to trough ; but 

 the discovery of specimens on wild fish caught in Craig Pond at 

 the head of Craig Brook, more tlian half a mile distant, with in- 

 tervening falls of great difficulty, indicated that the parasite was 

 native to our locality, and suggested that something extraordin- 

 ary in the condition of the lake trout invited the attack. Indeed 

 it seems not impossible that the fish died from some other cause, 

 — some unknown disease, — and that the parasites had merely 

 been feeding on the disintegrated tissues. Verily, this is a case 

 in which judgment must be suspended. 



The most destructive disease that has ever come under my 

 observation was the sac-epidemic which raged several seasons at 

 Craig Brook and in 1892 destroyed 99 per cent, of our yoimg 

 Atlantic salmon. I call it "sac-epidemic" Ijecause it raged dur- 

 ing the sac stage of the fry, and because the most ob^■ious symp- 

 toms were connected with the sac. It would appear about mid- 

 way of the sac stage, while the sac was still less than half ab- 

 sorbed. In water of constant temperature, such as pure spring 

 water, I imagine that the disease would appear by the first quar- 

 ter of that stage. Our water is very cold at the time of hatching 

 — about April 1st, — and gradually warms up, so that the develop- 

 ment of the embrvo is at first very slow and later comparatively 



