REACTIONS OF FISHES TO SALTS 275 



indicates that the antagonism between the salts of calcium and 

 magnesium is not nearly so marked as it is in the case of the 

 salts of sodium and potassium. Since the former salts are by 

 far the most common and plentiful in natural fresh waters, the 

 importance of salts in nature in antagonising introduced acids 

 is less than it would be were the salts of sodium and potassium 

 plentiful. The problem is one which will furnish material for 

 some very interesting ecological investigation. 



The importance of small amounts of ammonia in natural 

 waters has been pointed out in the discussion of these salts. 

 The effects of starvation upon fish metabolism and reaction 

 will be further discussed in another paper. There is an inter- 

 esting possibility brought out by the acclimatization and other 

 data, especially those pertaining to the importance of acids, 

 that will be discussed here. This possibility relates to the 

 movements of organisms in general but the present discussion 

 will be limited to the very interesting migrations of the anadro- 

 mous fishes. 



The stimulus that causes anadromous fishes to spend part 

 of their life cycle in fresh and part in salt water has long been a 

 matter for speculation. Such stimulus must be related to the 

 rhythmical metabolism of the animal, for it brings the fishes into 

 the sea or fresh water at certain definite stages in tl;e life cycle. 

 The state of the metabolism of these fishes while they are in the 

 fresh water, must differ very decidedly from that during the period 

 of the life cycle which they spend in the ocean, for these two en- 

 vironments differ in two very important particulars, namel^^, 

 the fresh water has a low specific gravity and is consistently 

 acid in reaction, while the sea water has a relatively high specific 

 gravity and is consistently alkaline. Also the reactions of the 

 fishes are markedly different. In the fresh water they are posi- 

 tive to current, and, in a gradient, select water that is just on the 

 acid side of neutralit}" and of lower density than that of the sea. 

 Salt water fishes, on the other hand, are probably negative to a 

 fresh water current, select water on the alkaline side of neutrality 

 and reject water of low specific gravity for that of higher (Shel- 

 ford and Powers '15). The reactions of the fishes in fresh water, 



THE JOURNAL OF EXPEKIMEXTAI. ^OOLOGY, VOI,. 19, NO. 3 



