Mr D. Ellis on tite Natural Hutory of the Salmon. 267 



deal more fish, which did not then float up so high as the upper 

 nets *. Many otlier witnesses give a similar testimony, as to 

 the refusal of salmon to enter rivers when much heated. The 

 temperature of the sea is probably that best suited to the econo- 

 my of these animals ; and those rivers, therefore, which come 

 nearest to that temperature, will probably be preferred by them ; 

 and as the ordinary heat of fishes is very near to that of the 

 medium in which they live, a temperature, either much above 

 or below that of the sea, is, in all likelihood, unsuited to their 

 nature. 



If, however, freshes and floods occur in any particular river 

 during the hot season, salmon then move up them, even many 

 'months before the spawning season. Some of these may re- 

 main in the upper parts of rivers, if they find water sufficient 

 to harbour and protect them, until that season arrives; but 

 others, as we have seen, avail themselves of subsequent floods to 

 revisit the sea, in which alone they may be said to thrive. It is 

 not, however, the freshes and floods in all rivers that induce 

 salmon to enter them ; for sometimes the water brought down 

 certain rivers, is impregnated with matter disagreeable to the 

 fish. The rivers Ness, Ewes, Shin, and Thurso, says Mr 

 Stevenson, supply the earliest fish in Scotland : the Tweed and 

 Tay also supply early fish, but not so early as the former rivers. 

 Now, the four first rivers are discharged from the largest lakes 

 in Scotland, and in these lakes the water is purified before it is 

 sent down the rivers, in the winter and spring months. So like- 

 wise the Tweed and Tay nm principally through clayey soils, 

 and their waters, in spring floods, are not impregnated with 

 matter disagreeable to the fish. But rivers which run through 

 a mossy district, and discharge their waters into the sea, with- 

 out previous purification in large reservoirs or lakes, as the 

 Findhorn, Conon, Beauly, Spey, and many others, — such rivers, 

 when swollen by the melting snows in the spring months, are 

 turbid and disagreeable to the salmon until about the month of 

 April, when they begin to discharge light spring rains, sweet, 

 and comparatively free from the impurities of an earlier period. 

 It is then only, he adds, that these latter rivers begin to yield 

 fish, that is, not till the lake-rivers are beginning to fail ; indeed, 

 > • Beport I. p. 72. 



