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 liable, 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- 
sults 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 
