212 BRITISH FRESH-WATER FISHES 



stock has brought about the disease. Ten per cent, of diseased 

 fish upon a stock of ten thousand salmon will amount to one 

 thousand a shocking display of mortality ; but ten per cent, 

 upon five hundred salmon will result only in fifty diseased fish, 

 which a single flood may carry away to sea without attracting 

 any notice at all. I have seen salmon as badly diseased in 

 rivers where they were exceedingly scarce as in rivers where 

 there was a heavy stock ; and, on the other hand, I have seen 

 shallow Loch More, at the head of the Thurso, crowded with 

 salmon throughout a hot summer, yet the salmon disease has 

 never been reported from the Thurso at all.* 



Although all salmon spawn in the autumn and winter 



months, covering a period from the middle of October at 



f earliest to the end of January at latest, there is a 



Early and . . J . 7 .' . 



Late Salmonsmgular and hitherto inexplicable variation in the 



time of year at which they begin to ascend different 

 rivers. Into some rivers salmon enter in greater or less 

 numbers in every month in the year, nor is this dependent 

 upon the size of the river, because it is the case both in the 

 mighty Tay and the puny Thurso. Into some rivers salmon 

 begin to run early in spring, while in others fresh-run fish are 

 never found till summer or even autumn ; neither does this 

 seem to be connected with the volume of the stream, as is 

 shown in the case of the Bann and the Bush, rivers of Ulster, 

 debouching at a distance of about ten miles from each other. 

 The Bann is a noble river, flowing out of the Lough Neagh, 

 the largest sheet of fresh water in the United Kingdom, and 

 here, if anywhere, one might expect early salmon to run. Yet 

 not a fresh fish may be looked for in the Bann before the 

 month of May ; whereas in the Bush, an insignificant ditch 

 compared with the other, flowing out of no great reservoir, but 

 draining the peat-mosses of Antrim, salmon put in an appear- 

 ance in February, and are caught in great abundance in March 

 and April. 



* See Appendix, p. 305. 



