38 



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 

 a fourth of the quantity for the same number of Fontinalis 



