NOTES ON THE SALMON DISEASE. 349 
old anglers for many yaars past in isolated cases of salmon dying 
by fungus. But it was not till 1878 that it first appeared in the 
Solway as a widespread and fatal epidemic—when thousands of 
salmon died. Then it ravaged the Tweed, Nith, Annan, Doon, 
and Derwent, reaching from the Severn to the Tay ; and although 
at present it is not quite so vigorous in its progress, yet it has, 
by latest accounts, appeared in the Northumberland Tyne, a 
river which has hitherto enjoyed a singular immunity from it. 
In the United States it has long been known in the rivers of the 
Pacific coast—in fish hatcheries,—and latterly I see it has ap- 
peared in Canada. Here in New Zealand a fungus was observed 
by Mr. H. Howard in 1876 on trout in his pond, and I have 
seen it myself on a golden carp at our Opoho ponds, also on 
large trout in Lake Wakatipu—to which I shall refer again. 
Although the above places are not the only ones where disease 
has appeared, both here and in other countries, yet they serve to 
give some idea of the wide distribution of this fungoid disease ; 
and here I ought to add that the seasons immediately preceding 
and during the outbreak of the disease till 1881 (which was a 
wet one) were remarkable for drought, heat, and lowness of rivers 
in Britain. 
I will here, in this connection, make some remarks on the 
nature of the waters in which the disease has been fatal. The 
Tweed drains an area which is partly pasture land and partly 
land highly cultivated ; but it has no lakes of any size. It isa 
fact also of great significance that within thepresent century the 
average flowof waterin the Tweed has decreased by about one-third 
—that is to say the discharge of the river (exclusive of floods) is 
two-thirds of what it was 60 or 70 years. At that date a 
flood took a week to run off, and thereafter the flow in the river 
diminished very gradually ; now a flood runs off in two or three 
days, and is higher while it lasts. The cause of this great altera. 
tion is the extensive drainage and agricultural operations carried 
out during above period. The effect of the change is that salmon 
cannot get up the river to spawn, nor out of it and back to sea 
when spawned, so freely as formerly. This, together with the 
obstruction caused by rivers, is the first or primary contributing 
cause of the disease, and means also less water, less oxygen, 
and more heat—all very bad conditions. But add to this the 
effect on the constitution of the salmon, of its prolonged passage up 
and residence in the river after spawning, and we have the jfirs¢ 
proximate cause of the appearance of the disease. Then the 
absence of the proper proportion of salt in the water seems to 
me to be the second cause. This of course I cannot prove directly ; 
but the healthy effects of salt on Salmonidz have been deter- 
mined. But there must be yet another or ¢hzrd cause, arising 
from the greatly increased nitrogen in the rivers, due to the 
decomposition of manures, both artificial and from the farm- 
yard, now so much more extensively used than formerly in agri- 
culture. These three predisposirg causes I shall refer to again ; 
but, together with these, the spores or seeds of the fungus, it 
