Fow to obtain tt. 163 
Dr. Day records (British and Irish Sa/monide, page 41) an 
interesting experiment which he tried “in order to ascertain the 
effects of direct concussion on ova. A number were dropped 
from various heights, or direct into the water, when it was found 
that in those in which this was tried within twenty-two days after 
being obtained from the fish, none lived over eight or nine days.” 
During the first stage of the ovum after impregnation it will bear 
a reasonable amount of concussion, but after a period of some 
thirty-six hours, varying according to temperature, a very slight 
amount will suffice to destroy the vitality of the embryo. It 
naturally follows that in cases where the latter is not killed it 
receives serious injury which will tell upon its after life. 
I remember a tray of eggs getting accidentally shaken on one 
occasion when incubation had proceeded for nine days, and 
although the accident at the time seemed trifling and the con- 
cussion was slight, yet within a few days over twenty-five per cent. 
of those eggs were picked off dead. After the eggs are well eyed 
concussion does not seem to kill them as in their earlier stages, 
but it produces injuries which often seriously effect the after life of 
the fish. 
The cure for sediment is an efficient filtering apparatus. 
Should it, however, from any cause settle upon the eggs, they may 
be washed after they have reached a certain stage, but care should 
be exercised in the operation. It is not safe to attempt it much 
before the eye spots appear or when the eggs are about half 
incubated. It may be done earlier by an expert, but the safest 
plan is to leave it until the eggs will bear moving. The water 
may then be lowered and a watering-can used, or they may be 
gently feathered over without lowering the water. 
The best plan of all, however, if there be much sediment, is 
to remove the eggs and wash them and clean out the hatching 
boxes thoroughly. To do this it is desirable to have one hatching 
box at liberty, which should be made ready for eggs. Then the 
contents of another box may be lifted out a grille at a time with 
the eggs upon it. It is needful to have a movable tank or vessel 
capable of receiving a grille, and this being filled with water, one 
may be placed in it and reversed and then another, and so on. 
The tank used for washing the eggs when first taken from the 
