EFFECTS UI'ON FISHES OF CHANliES IN SALINITY OF WATER. ()V> 



Erperiinent 38. 



Woods Hole, Septeiiihei', IHO-t. Tweiity-tive 7''. ///r/yV^Z/.v chano-ed daily from 



salt to fresh water, and vice vei'sa. No harmful results during the 8 days 



through which the experiment continued. (Compare with experiments 1 to 5.) 



Expert numU 39 and J^O. 



Woods Hole, August and September. VM)\. F. iliiq'lniiKis was used. In 



each case the elTect of this treatment was the deatii of a larger or smaller 



proportion of the fishes, though perhaps the daily handling had something to 



do with the result. 

 In experiments 3~ and 08 it was seen that no harm resulted from the alternation 

 of fresh and .salt water within the period of observation. Previous experiments had 

 shown, however, that fishes of the same species when left uninterruptedly in fresh 

 water sooner or later succumb. Giard (1900) narrates the ca.se of a stickleback which 

 lived in this way for many weeks. Rutter (1904) states that young Pacific salmon 

 when transferred from fresh water to diluted sea water fared better "when the 

 density alternated from low to high and back again."' There is an obvious parallel 

 I (('tween such fluctuations of salinity and those which i-esult from the ebb and flow of 

 the tide at a river's mouth. 



AOE IN KKI.ATIOX TO EXDl'KANCK OF (•HAN(;E OF MEDITM. 



According to Rutter (1904), the young of the (juiimat salmon could endure pro- 

 gressively higher degrees of salinitj" as they grew older, ranging fi-om •J.'') per cent 

 sea water at 6 daj's to practically pure .sea water at 2 months. 



Loeb (1894) records a similar correlation between the age of the embryo (jf 

 Fimdulus [heterocUtus) and the proportion of NaCl which could ))e added to the sea 

 water without arresting developnu ,it. 



Brown (1903) states that "there is a gradual increase in susceptibility to osmotic 

 changes and to the electric current as the embryo develops. "" H(> regards the latter 

 susceptibility as a function of the former. 



A considerable series of measurements of F. majalix failed to reveal any selec- 

 tive mortality in i"elation to size among fishes dying from the effects of fresh water. 

 Such a selective mortality was ver3' obvious, on the other hand, in the case of death 

 fiom asi)hyxiation, the "eliminated''' set having an average length about 7 per cent 

 greater than the "surviving" .set (i. e., those last to die)." 



ADAPTATION TO rHANOKS IN THE MEDIUM IN NATIKE. 



That many species in nature may be found in either medium is well known. 

 All of the anadromous fishes of course belong to this class, together with the eel 

 (cutadromous). Many other salt-water fishes venture into streams and may even 

 b(>come landlocked. Again, fresh-water fishes may be carried down to the sea by 

 freshets and survive in waters of consideral)le .salinity. In most cases it is impossi- 

 l)le to determine how abruptly the changes are made. The ascent of a large river 

 may occupy weeks, and during the earlier stages of the journey a zone of gradually 

 decreasing (generally of fluctuating) density is passed through. I am informed by 



"I hope befoFf long to present these results in a form whirh w\\\ meet tbertemiinds of the biometrieul critic. 



