28 On Stocking. 



But with a smaller size matters are very different. The least 

 portion of the yolk-sac slipping through which it does the 

 more easily, as the smaller the number of zinc the stronger the 

 current bulges out, and keys the fish on the reverse side of 

 the safety-screen in such a manner that escape is impossible. 



' At Howietoun the eggs are laid down to hatch between 

 nine and ten in the morning, and unless the day is very cold, 

 the hatch is completed by three in the afternoon, when the 

 shells are skimmed off and the water in the box heightened. 

 This is tedious work, and we do not care to hatch more than 

 a quarter of a million in one day, although it is occasionally 

 necessary to lay down a much larger number. After the shells 

 are skimmed off and the water heightened in the boxes, the 

 attention required is reduced to a minimum. As the fish 

 get stronger the current is increased, the regulating tap being 

 moved once a week through a space equivalent to one quart 

 per minute per box. Hardly any alevins die except in 

 experimental lots. The boxes themselves never require 

 cleaning; the alevins are their own housemaids. They are 

 constantly scouring over the bottom of the box, and keep the 

 charred wood polished like a piece of dark mahogany. The 

 current carries the dirt through the safety-screen, and it 

 settles in the space of 13 inches between that and the outlet. 

 The rough of this dirt is removed with a syphon every 

 morning. Once a week the cork in the settling-tank is drawn, 

 and the bottom of the box thoroughly cleaned with a brush. 



' The importance of exactly balancing the number of alevins 

 to the box, and adjusting the proportions of the hatching- 

 box to the current, are apparent. There is little danger of 

 having too many alevins in a box, as the number put in is 

 determined by the number of feeding-fry that can be properly 

 reared ; but if too few alevins are placed in the box, or if 

 they have been improperly incubated and have not sufficient 

 vitality, they will neither have strength nor activity to polish 

 the bottom ; and as with due deference to the opinions of 

 some perfect cleanliness at this stage is absolutely essential 

 to their future success in life, if they do not do their own 



