6 
dangerous extent on the dead ovum, and the saprolegonei 
hardly appearing at all, at least on the charred surfaces of 
the hatching boxes; but I now find by using a larger flow 
of water through the trays, and by increasing the flow 
during the latter stages of incubation, that with a tempera- 
ture of 45° Fah., fully 99 per cent. of Loch Leven Trout 
ova can be hatched into healthy well-formed alevins, and 
very nearly as good results. with the eggs of the Salmo 
Salar, the difference being probably due to the ‘difficulty 
of obtaining perfect impregnation in the case of ova taken 
from wild fish. 
Spring water seldom varies more than a few degrees 
even in very cold weather, and where it is used the 
duration of the hatching period can be accurately ap- 
proximated, which is often a great convenience. 
At Howietoun in the winter of 1878-79, river water fell 
within a degree of freezing, and remained there for three 
months, so that Trout ova took 105 days from being 
spawned to the first appearance of red blood, which 
marks the middle of the period of incubation. 
The quantity of water required in the process of incu- 
bation depends partly on the number of eggs, partly on 
the temperature of the water, and partly on the hatching 
apparatus used, but as I have hitherto only attained the 
very best results by the grille and tray system in the 
incubation of the eggs of Salmon and Trout, I will con- 
sider the water supply solely with reference to it, merely 
remarking that the quantity used in this system is greater 
than in any other; the result of eight seasons’ experience 
has been in favour of the supply of not less than ten 
gallons a minute for every hundred thousand Lochleven 
Trout ova; about a third more for Salmon ova, and only 
2 fourth of the quantity for the same number of Fontinalis 
