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 Ib. 

 are common, and those of 30 Ib. and 40 Ib. not unusual, while 

 instances have occurred of salmon weighing as much as 50 Ib. 

 At the western extremity of the Solway is the Cree, wherein a 

 fish of 20 Ib. is regarded as a prodigy. What becomes of 

 Cree-bred fish after they attain a weight, say, of j 5 Ib ? 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 at uncertain intervals in nearly all our salmon 

 disease. r i v ers. 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, 



