110 EEPOET OF THE COMMISSIONER OP 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 suflEi- 

 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 fall of 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 sufiicient 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 



