276 How to obtain it. 



worthy of note, and that is that trout vary very much more in fresh 

 water than they do in the salt. Some colours are also much more 

 permanent than others. The experiment is now pretty well 

 known of putting fish into a tank that is black and kept almost 

 dark. When taken out and placed in the sunlight in a white 

 bowl they look very black, but in a few minutes will often become 

 light in colour. This is also largely the case with wild fish 

 passing from lake to stream, or vice versa, or from one geological 

 formation to another. Much more so is it the case when the 

 migration is from river to sea, or sea to river; not only do the 

 colours and general appearance of the fish become changed, but 

 we find, in the case of fresh-water forms becoming anadromous, 

 and vice versa, that the various organs and parts become altered 

 also, probably by the law of adaptation. 



It is now an ascertained fact that trout (Salmo fario} can 

 become anadromous in their habits. This seems to be largely the 

 case in some of the rivers of New Zealand, and also in those of 

 Tasmania. In British waters instances of brook trout migrating 

 to the sea are common enough. I have examined many brooks 

 at low water, and have found beautiful little trout under the 

 stones between tide marks. Quite possibly this may have an 

 important bearing on the fine quality of the fish occurring in some 

 lakes in close proximity to the sea, as, for instance, Loch Stennis, 

 in Orkney. 



An interesting experiment was accidentally tried a few years 

 ago by the owner of a fish pond near the sea. He built a rather 

 elaborate outlet of heavy masonry, and carried it forward some 

 distance into an estuary, so that the tide rose and fell within the 

 walls. In it was placed a grating, which prevented fish passing in 

 and out. Now it so happened that a few trout passed down out 

 of the fresh-water pond above, and got into the tidal tank, which 

 always had some two or three feet of water in it, and at high 

 water a considerable depth. The water that entered from the sea 

 usually swarmed with small crustaceans, etc., and when the trout 

 were discovered some months afterwards they had grown to a 

 much larger size than any in the large pond above, notwithstanding 

 the confined area of the place in which they had been living. 

 This opens up a very large question as to the future possibilities 



