FOOD OF FISH AND ITS PRODUCTION. 99 



in size and improved in condition wonderfully; but it 

 is also fair to say, that they became much shyer of 

 rising to the fly. Probably the reason why the fish 

 sometimes rise well to flies, and not at others, in lakes 

 like those of Donegal (which are by no means few), is 

 owing to the fact that the abundance of caddis at the 

 bottom may be undergoing some transformation, into 

 flies perhaps, which ascend rapidly to the top of the 

 water, and the trout are thus led in pursuit of them 

 to the top of the water, where the insects rest, and are 

 easily captured. If anglers, being aware of this fact, 

 made some little study of entomology, so far as to know 

 about the time when these insects undergo their trans- 

 formations, they might not be induced to seek such 

 lakes so often in vain. In the instance I have noted 

 the lake is deep, and the water dark ; and the fish at 

 the bottom, engaged with ground food, do not see the 

 flies at the top. 



Again, I will instance the fish in Loch Leven 

 which grow to a large size, and are almost always in 

 superb condition. The bottom of the lake, in places, 

 is grown over with a peculiar weed ; in this is found 

 a great variety of insects, chiefly crustaceee, as small 

 snails of various sorts : the lake also abounds in the 

 more minute entomostracse. Large quantities of both 

 are often found in the stomachs of the trout when 

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