How to obtain it. 199 



it is desirable for anyone performing an experiment of this kind 

 for the first time to exercise a little care. Do it gently, and watch 

 the effect it has on the fish. Where the water is right, and all in 

 order, it will do no harm, but will be highly beneficial. It also 

 has a tendency to destroy any animal parasites that may possibly 

 be attacking the fish, even at this early stage. 



Paralysis is a disease to which young fish are iable, and its 

 presence may be known by seeing some of them come out of 

 the " pack," and lie very still as if dead, at the same time looking 

 very pale. They may be mistaken for dead ones, but on taking 

 them up in a dipping tube they will be seen to breathe, and an 

 occasional spasmodic movement of the tail may be apparent when 

 disturbed. They may remain in this condition for some time, 

 perhaps days even, but they will probably die, and if the cause be 

 not removed great loss may ensue. To prevent this disease 

 making its appearance, a good current and plenty of oxygen seem 

 to be the best specifics. 



The depth of the water in the hatching boxes at various 

 periods of development is a point that has been much discussed. 

 It is difficult to lay down any special rules for its regulation, as 

 what does not answer in one case has been found to give very 

 good results in another. Much depends upon surrounding cir- 

 cumstances, such as the nature and quality of the water, and its 

 temperature. A sufficient knowledge of these matters can only 

 be gained by experience, but it may be laid down as a general 

 rule that the deeper the water the greater supply of it that is 

 required. While a depth of four inches will give satisfactory re- 

 results with a flow of thirty thousand gallons a day through a double 

 supply hatching box, as at the Solway Fishery, at this stage the 

 depth of water must be decreased where the supply runs short. A 

 fine jet of air injected into the water has proved to be of service 

 in some hatcheries abroad, but the better plan is to provide a good 

 supply of suitable water. Where the upper ends of the hatching \ 

 boxes can be raised a little, the advantage of a varying depth is 

 obtained, but this is not always practicable. 



There is another disease which sometimes attacks young 

 trout, and it appears in the shape of a small white speck within 

 the umbilical sac. It is usually, if not always fatal, but does not 



