No. 645] 



FISH MIGRATION 



375 



successfully by Shelford, Powers and others in experi- 

 ments on temperature, acidity, alkalinity and salinity. 

 It proved too excitable for the experiments with which 

 the present work was concerned. 



Experiments 



Fresh Water and Sea Water. (Temperature 20° C.) 



With apertures f in. in diameter in two glass tubes 

 directing horizontal streams of fresh water and sea water 

 to a point six inches from the ends of the experimental 

 troughs, it was found that 10 fish responded during 25 

 trials in such a manner that 11.8 was the value for re- 

 sponses to fresh water and 44.6 was the value for the sea 

 water. These figures were obtained by multiplying the 

 number of fish responding by the feet traveled up the 

 trough towards the current, adding the total of 25 trials 

 and securing averages for control and experiment. 



The fish responded readily to the flow of water and 

 since there was an admixture of fresh and salt water in 

 the lower ends of the troughs, they did not at first dis- 

 crimiilate the sea water before reaching a point 6 or 7 

 feet from the pool, that is 3 or 4 feet from the intake. 

 As their reactions to the currents became established, 

 however, they came in smaller numbers and finally be- 

 came aligned along the sea water current at a distance 

 of not more than a foot from the intake. 



On changing the flow of fresh water to salt and vice 

 versa, it was noted that at first the fish came into the 

 trough formerly salt, and proceeded beyond the point 

 where they usually traveled in fresh water. This was in 

 part due to the habitual response and partly to the pres- 

 ence of some salts in the trough. On reaching the intake, 

 they rapidly returned to the pool, one or two pioneered 

 in each trough, then the whole group explored the salt 

 trough and finally came to a point near the salt water 

 intake. 



