110 REPORT OF THE COMMISSIONER OF FISHERIES. 
At the Nashua station the investigations were continued in the spring 
of 1904. They were directed chiefly to the water supply and consisted 
of determinations, made at the station, with field apparatus, of the 
dissolved air in samples of water taken from many different sources 
of the station’s water system. The results of these analyses show 
that the whole station water supply except the Pennichuck, or 
Nashua city water, has an abnormal content of dissolved air. All such 
sources of supply are abnormally high in nitrogen and some of them 
are at the same time deficient in oxygen. The constantly flowing sup- 
ply is mainly from two sources, one being artesian wells, the other a 
large reservoir pond fed chiefly by springs. This latter supply is in 
somewhat better condition by the time it reaches the fish ponds or 
troughs than is the artesian supply. In no case is the excess of nitro- 
gen very high, and in only a few is the deficiency of oxygen very 
great, but either is enough to cause some loss of fish and the effect of 
the combined evils is believed to be mainly responsible for the mor- 
tality among younger fish at the station and for the poor condition of 
some of the adult stock. 
The fact that water with an excess of nitrogen is unhealthful for 
fishes, and that it may be corrected and rendered harmless by a suffi- 
cient exposure to the air, is shown more by the experience at the 
Woods Hole station than at Nashua. At Nashua it is not easy to apply 
this remedy on a large scale. One experiment, however, indicates 
that it has a like effect. Two troughs, each containing 6,000 to 7,000 
brook-trout fry, were supplied with water form the reservoir pond. 
One was lowered to the ground and the water entered it from a box 
with a finely perforated bottom and after a fallof some 3 feet. In the 
other, the water entered more directly. At the end of nine days the 
loss in the former trough was 645; in the latter 2,583. The exposure 
of the water to the air had evidently reduced the loss 75 per cent. 
The device reduced the nitrogen and increased the oxygen, but not all 
the excess of nitrogen was removed nor did the water become quite 
saturated with oxygen. Without doubt, were the exposure process 
carried further, perhaps by one or two repetitions, all the excess of 
nitrogen would have been removed and the full amount of oxygen 
added, but on account of the lack of sufficient fall this can not be done. 
While a deficiency of oxygen is readily corrected by fall and exposure, 
it is with difficulty that an excess of nitrogen is completely removed. 
It appears, nevertheless, from the analysis of the creek outflow, which 
is the whole Nashua supply after it has flowed through the ponds, 
flumes, etc., that this water has been almost completely corrected of 
its air defects. Therefore it might be used again, and if the hatchery 
and ponds were moved to a point below, a good supply would be at 
hand. But this is not to be advised. If there were provided a fall 
considerably greater than at present is possible, and the whole station 
