l6o TENTH ANNUAL REPORT OF THE 



this excess is doubtless a thick growth of algae, chiefly a Spirogyra, which 

 lines the bottom of the pond throughout a large part of its extent, but is 

 heaviest about the middle. The algae during daylight absorb carbon dioxid 

 from and give off oxygen to the water. Just what effect an excess of dis- 

 solved oxygen has upon fishes is not known to the writer and is an interesting 

 field for study. But this effect is presumably injurious. A number of adult 

 trout were contained in the reservoir pond in question at the time of the 

 observations and were in good condition, but they had access to all portions 

 of the pond and in some of these no excess of oxygen existed as will be seen 

 by a reference to the table. Conclusions from these fish are not therefore 

 of much value. 



The excess was not great and was speedily dissipated, or very nearly so 

 by exposure to the air, so that by the time the water reached the nursery and 

 other ponds the oxygen content had fallen almost to the normal. It cannot 

 be said to have any bearing on the disease. 



Probably no natural waters are known to ever contain a deficiency of 

 dissolved nitrogen, but they may have an excess of this gas and this condition 

 is inimical to fish culture. An excess of three or four cubic centimeters per 

 liter is sufficient to cause death with marked symptoms and one to two centi- 

 meters will probably cause trouble though not necessarily with immediate 

 heavy loss. The Cold Spring Harbor waters have no excess of any practical 

 significance. Each sample of water taken close to its origin from the earth, 

 as the reservoir pond samples, does show a slight super saturation with nitro- 

 gen, in no case higher than 0.67 cubic centimeters per liter. A considerable 

 quantity of nitrogen gas is held mechanically in the gravelly bottom of this 

 pond, and this is probably responsible for the condition. In every case 

 where the same water has been examined after a thorough exposure to the 

 air, as in the fish ponds themselves, the nitrogen excess has been completely 

 removed. The figures in fact show a very slight deficiency but within the 

 limits of error of the apparatus used in the determinations, and all such 

 samples may be regarded as saturated. While, then, there is no nitrogen 

 defect in any of the station water when used for trout in the fish cultural 

 ponds proper, the water of an artesian well, ninety feet deep, not far from 

 the station grounds shows an excess of over two cubic centimeters per liter, 

 and would not be suitable for fish culture without deaeration by thorough 



