B12 REPORT OF THE COMMISSIONER OF FISHERIES, 
The selection of water supplies for fish cultural or similar purposes 
should include a careful scrutiny of their quality with respect to dis- 
solved air. There are the two opposite faults to be guarded against. 
When either is extreme in degree, its recognition will not be difficult. 
But it is probable that cases will occur, and have occurred, where either 
fault is but slight, and causes no heavy losses or marked symptoms on 
its own account, while it at the same time is responsible for a gradua 
and insidious lowering of condition among the fishes which makes 
them susceptible to the sudden and rapid epidemics of bacterial or 
protozoan infection, or to the less acute attacks of higher parasites. 
In such cases the certain recognition of a slight excess of nitrogen, 
with ordinary methods of gas analysis, may require the average of a 
number of determinations. The constant ebullition of gas in bubbles 
of moderate or large size from the water sources is sufficient to cause 
suspicion of a nitrogen excess, but the absence of such bubbles is by no 
means reassuring, for supersaturation may occur in the depths of the 
spring without any of the undissolved residual gas revealing itself at 
the surface. As for the oxygen, it is not known just what content 
short of saturation completely supplies all the needs of fishes, but 
since their natural abodes, and particularly trout streams, closely 
approach saturation (Hofer 1904, pp. 157 et seq.), it is well to lay stress 
upon the desirability of maintaining a high oxygenation in fish cul- 
tural waters. For trout, and particularly the brook trout, this is 
imperative. It is probable that most spring waters are not highly 
oxygenated. Usually they take up incidentally, in the conduits or at 
delivery pipes, more or less oxygen before they are actually used as a 
fish-cultural supply, and sometimes means of aeration are specifically 
provided. So important are these that it seems not too much to say 
that devices for this express purpose should be provided in all cases 
where spring or well waters are used for salmonoids, unless repeated 
quantitative determinations made at different seasons show that the 
water can not be improved. 
Tasie I.—Showing composition of gas delivered from the bottoms of ponds, springs, or 
' wells. 
[All gas determinations by M. C. Marsh save where otherwise stated. ] 
Percentage of— 
| 
Source of sample. | Date. 
| 
| : Remarks 
| Carbon |,;; SEES | een | : 
| dioxia, ae eal Oxygen. | 
SSS 2 | 
1. Spring at Fishery, Tenn..... May, 1903 | 0.8 82.5 | 16.7. Continual evolution of 
| | _ gas in large amount. 
2. Artesian Well, Nashua, N. H.| Sept.,1903 4 | 87.8 | 11.8 | Discontinuous evolution 
| | of gas in small amount, 
3. Fish cultural pond, Nashua, Sept., 1903 .8 82.8 16. 4 | 
INS ta | 
4. Reservoir pond, Nashua, | Apr., 1904 1.4 96.3 2.3 | 
Nee: : | | | 
Db. Springyn) Vermomtcce:. tc Sept.,1903 | Trace. 87.4 | 12. 6 | 
Nos. 1, 2, and 5 were determined by the Bureau of Chemistry. 
