MOVEMENTS OF HERRING AND OTHER MARINE FISHES. 33 1 



per 1. and the reaction was very sharply negative to fresh water. 

 The concentration of the carbon dioxide in the fresh water was 

 gradually lowered and the avoidance fell off as is shown in graph 

 12 which was really only a continuation of ii interrupted to take a 

 sample which showed the carbon dioxide content to be 8.1 c.c. 

 per 1. During the period represented by 11 the negative re- 

 action decreased gradually until a point was reached when the 

 tank was probably about equally acid throughout, after which 

 the fish became negative to the sea water at the end of 13 minutes 

 when on the basis of a uniform decrease the sea water which 

 usually contained a little less than 2 c.c. per 1., became more 

 acid than the fresh. Thus it appears that these fish are as 

 sensitive to acidity as litmus paper. 



The relation of the two species of fishes to salinity is inter- 

 esting in this connection. The salmon goes into fresh water to 

 breed and some may reach maturity there or they may return 

 to salt at varying ages. In connection with the entrance of 

 salmon into fresh water, the orientation of these specimens with 

 head in the fresh water is of interest but it is evident that the 

 orientation is with reference to acidity and alkalinity rather than 

 salinity. Sea water is less acid than fresh and the reactions of 

 the salmon accord with their recent entrance into salt water. 

 In the case of the herring, they are known to enter fresh water 

 and some remain there permanently. Lydekker^ states that 

 some of them will live in brackish water and become dwarfed. 



When carbon dioxide was used in sea water the avoidance of 

 the higher concentration was very striking, in all concentrations 

 tried, up to 70 c.c. per I. The avoidance was usually propor- 

 tional to the concentration with staggering in the very high ones 

 just as is the case with the fresh water fishes. 



6. Oxygen. 



The oxygen in the sea water in use at the station never reached 

 saturation. One experiment was tried with water drawn directly 

 from the tap, against water aerated by running over a board. 

 The fishes selected the aerated water. When oxygen was 

 added to the water used in opposition to that drawn directly 



1 New N. H., Vol. V., p. 489- 



