16 Conservation Department 



Gardner and Leetham (1914)^ determined experimentally the 

 asphyxial points for brown trout at various temperatures and pub- 

 lished the following data : 



Table 4. — Asphyxial Poixts for Brown Trout 



One may reasonably assume that these are not far out of the 

 way for lake trout. It is worthy of note that the asphyxial point 

 varies directly with the water temperature, an indication that the 

 requirements of fishes for oxygen are greater in high than in low 

 temperatures. Consequently the relation between depth and 

 oxygen content assumes greater importance. 



In Hemlock lake trout can undoubtedly inhabit regions down- 

 ward to 18 or 20 meters, showing temperature of about 9.8° C. 

 and oxygen content around 3 c. c. per liter. These are not neces- 

 sarily the lowermost limits but are undoubtedly close to them. 



In Conesus lake the oxygen is practically wanting at a depth 

 of 10 meters (Table 3). Trout could not live here nor at 9 meters, 

 where the asphyxial point is probably reached. In shallower water 

 wliere tlie amount of oxygen is sufficient the temperature is prob- 

 ably too high. We could reasonably assume from this that the 

 planting of lalve trout in Conesus lake woukl be a waste of time 

 and energy. 



Purity. — The purity of the water in a stream may often be 

 measured by its oxygen and carbon dioxide content. This applies 

 more particularly if decomposible organic substances are entering 

 at certain places. However, if the inpouring of such substances 

 is temporarily stopped, the purity cannot always be determined by 

 chemical tests. In such cases and also in others where the offend- 

 ing substances are inorganic and perhaps poisonous, a census of 

 aquatic organisms will often reveal the true conditions affecting 

 fish life. 



It would be useless to stock a stream from which food organisms 

 have vanished, even though the particular kind of pollution did 

 not actually kill the fish. Upper Knight creek is an exam})le in 

 which crude oil from adjacent wells has exterminated nearly every- 

 thing except certain minnows, crayfish and certain algae. 



\n Wolf creek, which fiows through Castile, the polluting sub- 

 stance is salt. Xo I'l-esh walei- fish conld sland the degree of 



' Oil tin- IJt'spiralory Iv\c1i;iiik<' in Fresh Wiilci- i'^isli. I'.in ("li 

 Vol. S. pt. II, i;)14. 



