CAUSES OF DISEASE IN YOUNG SALMONOIDS. 9II 



The unfertile eggs are not taken out, and the first filament of fungus may 

 not be seen on an egg that is in a corner of the grill. But later the eggs may 

 be covered with this delicate down, and although something might still be done 

 for the embryos whose breathing is thus interfered with, even the flow of water 

 has not been increased since the eye spots appeared, and so the fimgus establishes 

 itself. 



The hatching time is now at hand, and may last, in water having a tem- 

 perature of 10°, some ten or twelve days, and sometimes more. Until it is 

 over there is no thought of placing the fry in a cleaner "place. As the fry hatch 

 they fall, like the shells of their eggs, to the bottom of the trough, on a soft 

 velvet composed of the flourishing Saprolegnia. 



And these unfortunate fry, the gills of which have never ceased being in 

 forced contact with all the impurities and disease germs which line the bottom 

 of the trough, are now to be disturbed in this water, the sediment in which will 

 be visible to the operator when he shakes or moves the trough. Nor is it only 

 the breathing apparatus which suffers, but the entire fish, for its body receives 

 shocks and wounds, inviting the fimgus, and the mouth particularly becomes 

 infected. 



The disease then has secured its hold. It is not perceived, for the operator 

 believes that he has done all that is necessary by cleaning the fry at the close 

 of the hatching. They may have been replaced in the same trough after giving 

 the latter a hasty cleaning, for maybe there was no other at hand. Fry from 

 two different troughs may have been put together without thought of the 

 imprudence of this. The lots are then of different ages by ten to twelve days, 

 and they are a little crowded, there being 2,000 to 2,500 in those little troughs 

 without any increase of the flow of water — for how long? They will be fed in 

 a month, perhaps six weeks. In the meantime there is amusement in finding 

 a few monstrosities among them. These die from day to day and the yolk 

 sac sheds its contents, which adhere to the bottom and form white spots which 

 occasion no alarm. The Saprolegnia finds again a favorable bed for development. 



The oldest and most robust of the fry, endeavoring to move about a little, 

 reach a corner of the trough , where they crowd against each other. By their swim- 

 ming movements they form in this corner a small current, or more exactly, a 

 slight motion of the water sufficient to maintain them in equilibrium on their 

 yolk sacs facing this small partial current. As soon as the fry ceases to feel this 

 current it can not maintain itself on its yolk sac and falls on its side. Is it no 

 longer so strong? No; that is not the reason — it is the motion of the water 

 which is lacking and which does not exist in the trough in any other spot except 

 where the fry make it themselves. The proper motion of the water is created 

 by a device of mine which I shall describe, a siphon outlet system; but for the 

 present I say that the eggs in incubation were not given a current sufficient to 

 wash them, facilitate the exchange of gases, and keep them from being covered 



