216 FISHES 



may to some extent be to new water, also to the constitution or stock 

 of trout." I think it most probable that the food-supply was the most 

 important factor. The streams originally abounded with insects and 

 insect larvas (including various flies, as ephemerids, gnats, caddis-flies, 

 etc., grasshoppers and beetles), mollusca, crayfish and other Crustacea. 

 In many streams, and these are the streams which have lasted out 

 best as fishing streams, there were also countless shoals of minnows, 

 smelts and other fish. At first the growth was enormously fast, then 

 after a time the food supply gave out, and the big fish began to eat 

 the smaller ones, and gradually the lakes and streams became more 

 or less depleted. 



The extraordinary increase of imported birds which dates from 

 their first importation about 1868, and which was synchronous with 

 the increase of the trout, has also made a very great difference in 

 the food supply of the imported fishes. Grasshoppers, which were 

 remarkably abundant in 1868, are now comparatively rare, and this 

 is chiefly due, no doubt, to the increase of the starling; but smaller 

 insects, not so conspicuous to the ordinary observer, have suffered 

 equally. In this way it is certain that the insect-life of the streams 

 has been greatly reduced; while the trout ate the larvae, the birds fed 

 largely on the mature insects. In 1870 crayfish (Paranephrops) 

 abounded in nearly every stream; and I could collect quantities of 

 shrimps (Xiphocaris curvirostris) and amphiphods (Paracalliope fluvia- 

 tilis). The crayfish are now rare, and the other Crustacea are scarcely 

 to be found in any stream into which trout have been placed. One 

 of the problems which now faces those interested in keeping the 

 lakes and streams stocked with well-grown trout is that of finding and 

 maintaining a suitable food supply. The cultivation of suitable aquatic 

 plants (Potamogeton, Myriophyllum, etc.), and of insects, mollusca 

 and Crustacea, will be as much the work of a hatchery as the hatching 

 and rearing of the fish themselves. 



Mottram states that in New Zealand, on one occasion, the stomach 

 of a fish (Salmo fario) was filled with Spirogyra, Link; subsequently 

 it was proved that the fish took the weed in order at the same time 

 to capture a small Trichopterous larva. The yellow bloom of the 

 furze, Ulex europeetis. Linn., was also taken on account of a small 

 grub, probably one of the Tineina. 



On March 30, 1911, on Lake Okeraka, New Zealand, the stomach 

 contents of a trout were four grasshoppers, two cicadas, and three short 

 pieces of stick of about the same length and thickness as the grass- 

 hoppers. 



This is stated to show that the fish mistakes these things for the insects 

 on which it is feeding at the time. 



