CONTRIBUTIONS FROM THE BIOLOGICAL LABORATORY OF THE BUREAU OF FISHERIES AT WOODS HOLE. MASS. 



THE PHYSIOLOGICAL EFFECTS UPON FISHES OF CHANGES IN THE DENSITY 

 AND SALINITY OF WATER. 



Bv FRANXIS B. SIJIXKR, Ph. I)., 

 Dinr/or /■•is/irrii-s /.ahora/on; iraocla HoU; Mass. 



INTRODUCTION. 



It is !i oommonplace to both tishermaii und zpologist that certain tishes dwell exclu- 

 sively ill salt water and otluns oxclu.sively in fresh water, while others yet luay live 

 inditferently in either medium. It is well known, also, that death is frequently the 

 result of an abrupt and considerable chang'e of den.sity. 



Numerous i^roblems of great physiological importance are here involved. AA'hy 

 is an extreme change of density so fatal in some ca.ses and so harmless in others i 

 And is it the change of density which is responsible for the harmful effects, after 

 all; May not .saltwater be toxic, in a narrower sense, to fresh-water fishes, and 

 \ic(> versa? In any cage, what is the immediate cau.se of death? Are the limiting 

 membranes of a fish permeable to both water ajtid salts, or ai-e the}' only semiperme- 

 able ^ Or, are tliev, perhaps, impermeable 'to both? And are all of the limiting 

 membranes alike in this regard? Likewise,' is *heir condition the same for all spe- 

 cies and under all circumstances ? The.se are closely related ciuestioiis. They have 

 received many and cjuite contradictory answers. It is hoped that the experiments 

 discussed in tlie ensuing pages have contributed something toward their solution. 



The first of these experiments were chiefly concerned in determining whether a 

 given change in water density was harmful to a given species of fish, records being- 

 kept of the I'ate of death. In a second series weight determinations were made with 

 a view to ascertaining whether such changes in the density of the surroimding 

 medium were accompanied by appreciable osmotic efl'ects upon the fishes. Third, 

 it was sought to discover whether the membranes were permeable to water onl}' or 

 to salts as well. The passage of salts from tm fish into the surrounding water was 

 tested chemically, and likewise the salt content of the tissues of fishes of several 

 species under diflerent conditions was determined. Finally, a series of experiments 

 was performed with a view to di.scovering whether such osmotic exchanges were 

 confined to the oills or whether the o-cneral l)odv integument was likewise concerned. 



