964 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. 



The height of the water in the hatching-troughs should be carefully 

 attended to, so that it be liigh enough to have a current over the upper 

 trays but not high enough to let the bulk of the water flow over the tops, 

 depriving the lower layers of their share. If through neglect this rob- 

 bery takes place, a lot of eggs with white stripes across them will be found 

 some day, and close examination will show that the trunk of the embryo 

 in each one is white, opaque, and dead — sure symptoms of suffocation. 



The trays must be carefully watched, and those that rust be exchanged 

 for newly varnished ones. The change is easily made by turning the new 

 tray bottom up over the eggs, when, by a dexterous movement of the hands, 

 the two are inverted and the eggs fall upon the new tray. This should be 

 done over the broad pan, but the knack of doing it with very little 

 spilling is soon acquired. 



Strong light should not be allowed to shine for any great length of time 

 on the eggs. Total darkness is as good as anything. But if covers are 

 provided for the troughs, the house may be kept well lighted, and no 

 harm will come from leaving the covers of a single trough off long enough 

 to do any necessary work. In examining and picking the eggs, too, they 

 may be brought into a strong light. But sunshine should never touch them. 



13.— TEEATMENT OF THE FISH. 



After the eggs are all hatched the trays may be removed from the 

 troughs. The principal thing to be looked after now is that the fish do 

 not crowd up in heaps and smother each other. As soon as they begin to 

 move about a great deal the screens described above should be put in place 

 to prevent their congregating too much. If it becomes necessary to move 

 them about in the troughs, to disperse improper gatherings, or to get them 

 away from a spot that it is desirab]^ to clean, it can be easily done by ineans 



of a sweeping board, (Fig. 14.) This 



effective implement is simply a thin 

 board, a little shorter than the width 

 of the trouQ-h, with the lower corners 

 cut away as shown, so that they cannot 

 Fi'Tli. ' touch the sides of the trough and 



perchance catch and crush the young fry. It depends for its efficiency on 

 the fact that if a surface current is created in the trough in any direction 

 there will be a corresponding bottom current in the opposite direction, and 

 if this bottom current be moderately strong it will sweep along the young 

 fish with it. To move the fish down the trough the sweeping board is 

 placed in about the position shown in the cut and moved up the trough. 



If the young fish are to be set free this must be done as soon as the 

 yolk sack is absorbed, which will be from three weeks to three months after 



