Shelf ord. — Suitability of Water for Fishes 31 



havior of fishes plays a most important role (Shelf ord 

 and Powers '14) as is shown by the well known erratic 

 and commercially important migrations of the herring. 

 These fishes recognize slight deviations from neutrality 

 with a precision not excelled by litmus paper, and turn 

 back very constantly from acidity such as is given in 1 

 cubic centimeter of carbon dioxide per liter. Essential 

 neutrality is usually selected by herring. Twenty cubic 

 centimeters of carbon dioxide per liter in the presence of 

 oxygen to saturation is more quickly fatal to herring 

 than is the same amount to any number of fresh water 

 species. 



Decomposition in the sea nearly always takes place in 

 the presence of certain bacteria which yield quantities 

 of hydrogen sulfide. This is often accompanied by car- 

 bon dioxide and lack of oxygen. In shallow shore waters 

 it may exist in the presence of abundant oxygen and es- 

 sential neutrality because of the use of the carbon di- 

 oxide by the plants and their production of oxygen in 

 the process of photosynthesis. Fishes not only turn back 

 on encountering hydrogen sulfide but it is more quickly 

 fatal to them than any other gas of common occurrence. 

 Thus we must add the amount of hydrogen sulfide as an 

 index of the suitability of sea water. A good sea water 

 should not contain more than a trace of this gas. 



To summarize, we note that the amount of terrigenous 

 bottom and of free carbon dioxide serve as indices for 

 bodies of fresh water ivhile the amount of clean bottom, 

 carbon dioxide and hydrogen sulfide serve in bays and 

 enclosures of the sea. The determination of these gases 

 is not difficult provided one has a chemist make the re- 

 quired solutions. Contaminations such as sewage, or- 

 ganic wastes from slaughter houses, etc., influence the 

 water much as does an increase in the natural organic 

 matter and the indices apply where the commonest forms 

 of contamination occur. The writer is familiar with 

 cases in which these requirements have apparently been 

 met and still the body of water proved unsatisfactory for 

 the production of fishes, but in spite of these exceptions 



