192 THE COLOUR-SENSE IN FISHES 



veriest tyro, as he passes along the banks of a 

 clear trout-stream, will soon learn this elementary 

 fact for himself. As his education proceeds, he 

 will also speedily note that the trout's range of 

 vision is chiefly forward and upward ; and lying, 

 as they necessarily do when at rest, with their 

 heads up-stream, he finds that to approach 

 within reasonable distance unseen he must keep 

 down-stream from them and as low as possible. 

 This is the foundation of the first principle 

 of clear-water stream fishing, wading up- 

 stream. 



A much more intricate and difficult question 

 is that as to the power of discrimination of 

 colour by fish. Do they perceive the differences 

 of colour ; if so in what degree ; and do these 

 colours produce the same effect on the fish's as 

 upon the human eye? It is permissible to 

 assume that as fishes see, partly, at least, through 

 a different medium, the resultant impressions 

 received by them will vary from that in our 

 own experience. In the case of the angler's fly, 

 it will be generally seen by the fish against the 

 sky, that is, against the source of light ; and if 

 we hold a salmon-fly, however gaudy and bril- 

 liant, between our own eyes and the sky, we find 

 but a dark silhouette appearing, with possibly 

 reflected rays of coloured light from hackle-fibre 



