172 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



eggs would expose the youug fry to great dauger whenever there was 

 a thaw ill the tributaries where the water is not t\ armed from hot 

 springs. It is evident, however, on the other hand, that there is some 

 truth in the okl saying that lish in watercourses warmed by hot springs 

 get fatter than fish in common watercourses, as warmth increases the 

 lower animal life, and thereby produces more food for the fish. 



I have in several places in Iceland caught fish in watercourses whose 

 temperature was low, which had a very barren bottom, and whose t«ur- 

 rounding country was bare of plants and animals. Under these cir- 

 cumstances tbe number of fish was small, as they were obliged to go 

 over a large area to get their food. They were always half starved and 

 very lean. Their stomachs contained all kinds of small animals which 

 the wind had cast into the water, such as beetles, gnats, spiders, and 

 llies, and also all sorts of articles carried away by the water, as pieces 

 of wood, leaves, buds, &c. This shows plainly that, although these 

 streams may have a great deal of water, the number of fish in them will 

 be limited. 



There is another circumstance connected with these \streams which 

 should be noticed. They vary in course of time, often to such a degree 

 as entirely to change their character as fish-streams. The Norwegian 

 geologist Helland and the Icelander Thorvaldur Thoroddsen have 

 shown that those fiords into which mountain streams empty have grad- 

 ually been filled by the mud and gravel which these streams carry. 

 At the mouth of such rivers there are large masses of sand, which have 

 gradually filled the fiords into which these streams empty, while the 

 clear rivers empty into deep fiords with an unobstructed mouth. The 

 Ileradvatn has heaped up large masses of sand at the bottom of the 

 Skagafiord; the same applies to the Blanda; and the Hvita has carried 

 so much mud and sand into the Borgarfiord that, according to Thorodd- 

 sen's statement, small boats cannot enter when the tide is out. But 

 the salmon must have a free current and fresh water in the mouth of 

 the river which it visits; and wherever it finds saud-diifts, mud, &c., 

 it will keep away. It is evident that these circumstances, in rivers 

 like the Blanda, decrease the number of salmon. This is certainly more 

 likely to be the reason for this decrease than the casting of peat ashes 

 into the water, the digging of peat, or noise. 



The Iceland lakes are of considerable importance to the fresh-water 

 fisheries of this country, as they contain a vast number of trout and 

 mountain-trout, which form the object of fisheries, but not to such an 

 extent a8 might be desired. In some places the farmers go uj) on the 

 high plateaus to fish in the numerous lakes, and bring home a large 

 quantity of dried, salted, or fresh trout. It is a fact that the life of fish 

 in these, as in nearly- all the fresh waters of Iceland, is dependent on 

 the enormous masses of gnats anil flies found near them. The mount- 

 ain-trout, especially, lives on these insects and roots in the bottom, 

 which is filled with the larvte of flies. I have examined several fish 



