How to obtain it. 163 



Dr. Day records (British and Irish Salmonidce, page 4 1 ) 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 affect 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 



