64 Conservation Department 



universally small except a few at the head of the lake where the 

 abundance of weeds produces the shallow water organisms which 

 are necessary for their growth. 



Planting Lake Trout Fingerlings. — In order to determine 

 facts in the much disputed problem of how to plant lake trout fin- 

 gerlings two series of experiments were performed, one the first 

 week in July, the other the first week in September. Fingerlings 

 from the Caledonia hatchery were placed in an aquarium which 

 contained a liberal mixture of plankton and bottom organisms. 

 These fingerlings fed in about equal proportions on the larger 

 plankton, like Diaptomus, and Chironomus larvae. At the same 

 time fingerlings were placed in cages of wire netting at depths of 

 10, 30, 100 and 200 feet. Those placed at 100 or 200 feet were 

 raised the next morning and found to be in perfect condition. 

 They had also fed on Pontoporeia and copepods. The fish were 

 kept in these cages for an entire week during both series of exper- 

 iments and were found in perfect condition at the end. The fish 

 planted at 100 to 200 feet were more vigorous than those at 10 and 

 30 feet. The absence of Mysis in the stomach content of the fish 

 planted at 100 feet is undoubtedly explained by the fact that the 

 wire meshing was too fine for the Mysis to pass. Furthermore the 

 midge larvae did not enter because they confined their attention to 

 the bottom ooze which was outside the trap. We believe that the 

 trout would naturally feed on the larvae as they did in the aqua- 

 rium if they were free in the lake, and likewise that they would 

 feed on Mysis. This shows conclusively that young trout thrive at 

 depths of from 100 to 200 feet and find food successfully. The 

 temperature at that depth is that to which they have been accus- 

 tomed and the pressure has no effect on the fish, even when rapidly 

 lowered or raised from a depth of 200 feet. We believe, therefore, 

 that plantings of fingerling trout should be made in water exceed- 

 ing at least 60 feet in depth because the oxygen content is ade- 

 quate, the temperature is much more adapted to the young fish 

 than the temperature to be found in depths of 30 to 50 feet where 

 at the season of planting it is decidedly above the temperature in 

 the hatcheries to which the young trout are accustomed. Further- 

 more we find that the waters nearer shore to a depth of 50 feet are 

 inhabited by numbers of perch, bass and other predacious fishes 

 which would be a serious menace to the survival of the trout. 



The fingerlings should also be well scattered during the planting 

 so that each will have a better chance of finding a bountiful food 

 supply and predacious fishes will be less likely to devour a large 

 percentage of them. 



Several outstanding facts immediately engage the attention. 

 There are great areas of the lakes which are fit for fish propaga- 

 tion—a plentiful supply of oxygen, a low carbon dioxide content, 

 a plentiful supply of bottom fauna in most of the lakes and an 

 enormous supply of plankton Crustacea. The 50-foot con- 

 tour line is the general line of division between the realms 

 of the shallow water and deep water fishes. This is near the bot- 



