244 How to obtain it. 
Sometimes, instead of appearing emaciated, the fish which 
look quite healthy and well will suddenly commence drifting on 
to the screen in Jarge numbers. This is probably because their 
food has disagreed with them, and feeling sickly they are carried 
down by the stream, and will die if not removed. The best way 
of dealing with such fish is to place them, like their “lanky” 
brethren, in a suitable raceway, where many of them will recover. 
A raceway useful for this purpose should terminate, if possible, in 
a pond, in which the fish can remain, and which should contain a 
good supply of natural food. They will remain long enough in 
the raceway to receive much benefit, and on reaching the pond 
will be stronger, and the change of diet will soon put them right 
again. 
Many are the diseases to which trout are liable. A very 
sudden change of temperature will cause them to suffer from in- 
flammation of the gills, which is sometimes fatal; often they get 
over an attack of this disorder with the result, some people think, 
of deficient gill covers. This may be a consequence, but I rather 
think that fungus is much more to blame for it. The fungus is 
apt to grow on the edge of the gill covers, and although it may be 
afterwards cured, yet it interferes with the development of the 
opercula, which become permanently shortened in consequence. 
Young trout sometimes suffer from parasites, and when such is 
found to be the case a salt bath is beneficial, and will usually put 
matters right, though sometimes several applications are necessary 
before the desired end is obtained. I have occasionally seen 
several cases of blindness amongst a lot of trout. It attacks the 
best and finest fish in the pond, and they become very light in 
colour. The strangest part of the malady is that they do not, at 
least for a while, fall off in condition. They are easily picked out 
at a glance from amongst the other fish, and are not worth keep- 
ing. When old fish become blind it has the effect of making them 
dark in colour and inferior in condition. Probably this is because 
they do not so readily adapt themselves to circumstances as younger 
fish do. I have séen the latter feeding freely, and evidently guided 
to their food by the senses of touch and smell, and they get very 
expert at finding food without taking much exercise. This accounts 
for their keeping so long in good condition. 
