Originally published in Nature 133, 495 (1934) 



48, DIPLOGEN AND FISH 



G. Hevesy and E. Hofer 

 From the Institute of Physical-Chemistry, University- of Freiburg 



In recent months we have been carrying out experiments on the be- 

 haviour offish in heavy water. We find that goldfish (Carassius auratus) 

 behaved quite normally in the heavy water in which they were kept. 

 As heavy water was to be used as indicator of normal water, we had to 

 carry out our experiments in water containing only 0.5 mol. per cent 

 of diplogen, and it is therefore still possible that a higher concentration 

 of this isotope in water exerts effects upon fish. 



The aim of our experiments was to follow the exchange of water 

 between the fish and their surroundings, using heavy water as an indi- 

 cator of the movement of the total water. The use of radioactive iso- 

 topes for such purposes is well known. While the latter are practically 

 chemically identical, and as such are entirely trustworthy indicators, 

 that is not the case with the isotopes of hydrogen. Heavy water is, 

 therefore, only to be used with great caution as an indicator of ordinary 

 water. However, when using very dilute solutions of heavy water, we 

 may expect that the rate of exchange of heavy water molecules between 

 the fish and its surroundings w ill not be very different from that of the 

 normal water molecules. By measuring the speed at which the heavy 

 water enters the body of the fish we can therefore conclude at what rate 

 approximately the exchange of water between the fish and its surroun- 

 dings takes place. 



Some twenty fish having a total volume of about 10 cc. were kept in 

 about 60 cc. of water containing 0.5 mol. per cent diplogen water. After 



Table 1. 



Rate of Entrance of Heavy Water into Fish 



Time in hours 



Decrease of the heavy 



water content of the 



surrounding water 



Decrease expected in tlie case of 



equal distribution of the heavy 



water between fisli anil surroundin;^ 



water 



