Fish- Hatching in a Ctirrent of Water. 101 



which conducts the water from one box to 

 the other, and which, by being spread out 

 in a thin sheet, gets aerated by being brought 

 into contact with the atmospheric air. On 

 the bottom of these boxes two or three inches 

 of gravel is placed, so that the water runs an 

 inch in depth above the ova, which are distri- 

 buted over the gravel. The gravel should be 

 about the size of split peas ; if larger, the 

 alevins bury themselves in it, and when they 

 die cannot be seen, and when decaying will 

 foul the water. If the gravel be smaller, when 

 the watering-pot is used the shower drives it 

 about too much, and buries the ova, and when 

 any die they will produce the dangerous 

 byssus, with the risk of injuring healthy eggs. 

 A shallower box than that mentioned would 

 suit the hatching better, as half an inch of 

 gravel is sufficient — the object of using the 

 gravel being to retain the ova in their places, 

 and to keep them from drifting about with the 

 current, too much motion being injurious to 

 them. When the fish are hatched, however, 

 more depth is required, as the young fish soon 

 become lively, and may jump out of the hatch- 

 ing-boxes, and a deep bed of gravel is useful 



