Proceedings. 61 



have not apparently died of Saprolegna. It is when the 

 ordinary conditions of life are changed that they die of this 

 pest. Also the change from cold to heat seems to induce 

 the disease. The Sticklebacks mentioned above were taken 

 from ponds round Loudon, and exposed to the sun in shop- 

 windows ; and the temperature would probably be 75° or 80° 

 by day, while the pond would be 65° in summer at most. 



Sometimes the Dace die in great numbers in the Thames in 

 summer ; the gills are choked with Saprolegna, and the summer 

 heat is the probable cause. When Cliarr are caught in Win- 

 dermere they are taken from a depth of 60 to 100 feet, and 

 are put in boxes under water at Waterhead to be taken out 

 and sold by degrees. These fish are instantly attacked, and, 

 I grieve to say, the fishermen, knowing the fatal nature of 

 the case, always pick out the most diseased fish to sell first. 

 Now this does not come from change of pressure from one 

 hundred feet of water to two or three. When the change of 

 pressure affects a fish prejudicially it swells the aii'-bladder, 

 the fish comes to the top, and remains there till the bladder 

 either bursts or adjusts its muscles to the relieved pressure. 

 Perch taken m winter from the deep water of Skelwith Pool 

 generally burst the air-bladder when put into the bait-can. 

 I never saw a sign of this in Charr, though coming from 

 water so much deeper, nor did they seem inconvenienced by 

 the change. I once took twenty Charr from Windermere and 

 put them into a tank with a stream of spring water running 

 through it ; in four days Saprolegna appeared on all, and they 

 died. These Charr were taken in winter before the fence 

 laws came in, and I have little doubt that the change was 

 from cold to heat ; for the winter temperature of the depths 

 is always 38°, and, as Charr are not taken in cold weather, 

 the temperature of the shallows would jDrobably be about 

 45°, and my tank would be much the same. As Charr are 

 inhabitants of deep lakes only, this question of temperature 

 is probably of vital importance to them. 



I never saw a Trout affected ; but Trout are singularly 

 hardy and adaptable fish, requii-ing only one thing, and that 

 imperiously, namely, well oxygenated water ; all other things 



