296 How to obtain it. 
The further the fish go up rivers of any magnitude the worse it 
seems to be for them. Some races or species seem to go up the 
rivers only a short distance, whilst others go rather further, and 
others again will go more than a thousand miles if they get the 
chance. One thing is very certain—“ From the time the salmon 
enters fresh water it begins to deteriorate in flesh, and undergoes 
changes in form and colour.” There is a marked difference 
between a newly-run fish and one that has been in the fresh water 
for some time. There is one fact that is specially worth noting, 
and that is that when the fish running up these large rivers enter 
a tributary, and soon find it blocked up by an impassable fall, 
they will there deposit their ova, whereas had they held on their 
course up the main stream, they would probably have travelled 
hundreds of miles further. 
When salmon have done spawning, the sooner they get away 
to the sea the better. Detention in the river is evidently very 
bad for them, and they are at such times predisposed to attacks 
of fungus (Saprolegnia). As sea water is fatal to it, those fish 
which succeed in reaching the sea before they are attacked are 
freed from further risks, whilst those which have the fungus 
actually on them are cured in such cases as have not gone too 
far. Saprolegnia is somewhat similar to the fungus of diphtheria, 
and that is very amenable to medical treatment, if taken in time. 
On the other hand, in cases which have gone too far, or that have 
been neglected, death usually results. The same applies to 
Saprolegnia—the treatment is the same, the result is the same. 
On a fish farm it is usually plain to an expert at a glance whether 
a fish, if properly treated, will live or die. Every fish culturist 
has cases occasionally of Saprolegnia. It is one of the commonest 
diseases among fishes under certain favourable conditions, and it 
is much better understood than it was a few years ago. As I have 
already alluded to it in my chapter on pond life, it would be out 
of place, however, to go further into the matter here. 
I regret to hear that some of the American salmon rivers 
have recently been depopulated by the pollution of the water by 
the lumber companies. Enormous quantities of sawdust being 
sent down some of the streams, the salmon have been absolutely 
driven out of them. 
