EFFECTS UPON FISHES OF CHANOES IN SALINITY OF WATER. lUl 



HISTORICAL REVIEW. 



The work of Bert (1S71, is73, issH) has been more than once referred to in the 

 ])reeeding- pages. Bert's exphmation of the ''mechanism of death" in the case of 

 tl)e fishes studied by him deserves some attention. This writer explained the fatal 

 etlects of salt water upon fresh-water fishes by assuming an osmotic action upon the 

 gills. Tiie eapilluries of the latter became contracted, and the blood cells, distorted 

 by the action of the salt water, soon plugged them up and thus arrested the branchial 

 circulation. The immediate cause of death was thus believed to be asphyxiation. 

 In the case of scaly fishes, this occurred, he Vielieved, before any considerable amount 

 of water was abstracted from the body osmotically and before the blood in the larger 

 vessels was altered to any appreciable extent. With naked-skinned fishes, on the 

 other hand, osmotic action occurred throughout the entire surface of the body, and 

 the consequent loss of water from the tissues was one factor in causing death. 

 Bert is not entirely consistent in his views, however, for he likewise tells us that 

 "death is definitely due to the chlorides, "" and '"inversely [referring to the death of 

 salt-water fishes in fresh waterj it is the suppression of the sodium chloride which 

 causes death." This salt he found could not be replaced by any other substance 

 which he tried. Thus, the importance of chemical factors is recognized by him, 

 though he denies that the salts in sea water act as poisons to fresh-water fishes. 

 The differences in the reactions of different species of fishes are "due to differences 

 in the chemical composition of the branchial epithelium and in the exosmotic prop- 

 erties of this epithelium." 



Mosso (1890) also held (for sharks, at least) that the death of the fishes, when 

 placed in fresh water, was the result of asphyxiation due to the blocking of the gill 

 capillaries l\y disintegi'ated blood cells. In such a fish he found it impos.sible to 

 force salt solution through the branchial capillaries, though this could be done 

 readily in the normal animal. Mosso likewise records differences in the resistance 

 of the bloo.d cells of various fishes to the liamiolytic action of dilute salt solutions, 

 implying that such differences may be accountable for the relative power of these 

 animals to withstand changes in the density of the medium. In the case of certain 

 migratory fishes, which inhabit either medium {Aripi-nscr, Salmo, Anguilla, Petro- 

 iiiyzoi)) he found the corpuscles to be particularly resistant, being able to remain 

 many hours in a salt solution as dilute as 0.3 to 0.4 per cent without giving up their 

 hicmoglobin. Sea fishes as a rule he found to have less resistant corpuscles than 

 fresh-water ones. Other investigators (Hamburger, 1887; Bottazzi and Ducceschi, 

 1896, and Rodier, 1899) have performed similar experiments upon the erythrocj^tes 

 of various fishes, likewise finding great differences in their resisting powers, though 

 not in all respects agreeing with the determinations of Mosso. 



Of course any such effect of the surrounding medium upon the cells of the blood 

 presupposes some way by which it ma}' reach them. Bert believed that in fishes (at 

 least the scaly ones) death occurred before any considerable portion of the blood was 

 affected, the osmotic effects being restricted to the gills. 



In any discussion of the effects of changes in water density upon a(iuatic organ- 

 isms, the osmotic factor must play a leading part. Much light has in recent years 

 been thrown upon the osmotic relations maintained between the '"internal and 



