210 BRITISH FRESH-WATER FISHES 
operations can be conducted on a larger scale, no definite 
result can be obtained. 
The question suggests itself, why should salmon reared in 
the Thames return to it from the sea, instead of seeking 
another river? Some fishermen maintain that salmon always 
keep to the river in which they were hatched, and the proba- 
bility is that most of them do so. But instances, too numerous 
to detail here, have occurred of individual fish, marked in one 
river, having been retaken in another. It has to be considered, 
also, that the average size of salmon varies considerably in 
different rivers. If we take the Solway district as an example, 
we find the Eden at its eastern extremity, where fish of 20 lb. 
are common, and those of 30 lb. and 4olb. not unusual, while 
instances have occurred of salmon weighing as much as 50 lb. 
At the western extremity of the Solway is the Cree, wherein a 
fish of 20 lb. is regarded as a prodigy. What becomes of 
Cree-bred fish after they attain a weight, say, of 15 lb? It is 
not probable that they are a distinct race from the Eden fish ; 
it is more likely that when they reach that size they desert the 
Cree and fall in with the other large fish which make for the 
Eden. The problem must wait for solution till the systematic 
process of marking kelts has been carried further and till our 
knowledge of the movements of salmon in the sea is less 
rudimentary. 
It was in the year 1877 that attention was first drawn 
to what was considered a novel epizootic disease which 
attacked salmon in the Esk and Nith, and destroyed 
great numbers of them. Since that time it has appeared 
Salmon @t uncertain intervals in nearly all our salmon 
disease. rivers, The first outward indication thereof is in the 
shape of whitish patches on those parts of the skin which are 
not protected with scales, such as the head, the adipose fin, and 
the bases of other fins. These patches spread, become con- 
fluent, and form deep ulcers. The fish becomes quite weak 
and stupid, covered with whitish ulcers on the head and body, 
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