No. 645] 



FISH MIGRATION 



377 



well the attractiveness of the mixed solutions. With an 

 m/10 solution of MgClg plus MgSO^ and fresh water as 

 control, the record was 11.2 for the control and 34.2 for 

 the mixture. Again, in the case of KCl plus NaCl in 

 m/10 solution, the score was 31 for the control and 17 

 for the mixture. With double sea water (specific gravity 

 1.050) and ordinary sea water at 20° C, it was found 

 that the fish were attracted at the ordinary pressure and 

 temperature, reacting to the stronger solution an average 

 of 19.3 and to the control sea water 17.8 times. Furtlier 

 experiments should be run to determine the influence of 

 antagonistic action of the salts in pairs. Whether or 

 not the results will coincide with the results of permea- 

 bility experiments will probably depend somewhat on the 

 factor of temperature (Loeb and Wasteneys, 1912). 



Influences other than Salts 

 The foregoing experiments indicate clearly that the 

 behavior of the fish under consideration is materially af- 

 fected by the salts with which they come in contact in 

 fresh water. However, the factors involved in tlie )iiigra- 

 fion of fish are by no means thus ex])l<'iiiuMl. It i> worthy 

 of note that the reactions of Fitndulus hrtcntclifit.^ to 

 toxic salts or even sewage are dependent on temperature 

 and stream pressure. 



Temperature 



Numerous experiments were tried with varying tem- 

 perature and it was found that a temperature greater 

 than 23° C. repelled the fish and caused them to align 

 themselves along the current of fresh water at 20° C. in 

 preference to the slightly warmer sea water. 



With a reduced temperature, even one degree less than 

 the control (19° C), the fish were m.arkedly attracted. 

 In fact it was possible to lure them into double sea water, 

 KCl or fresh water if these were presented at the proper 

 temperature. Further experiments and observations are 

 necessary for these and other specier, in order to deter- 

 mine the relation between gonad development, bodily 

 condition and the responses to temperature change. 



