82 Bl'LLETIN <1F THE BUREAU OF FISHERIES. 



there is apiwrently iio decrease in the salt content of th(> body. (See experiment 



Bert (1871) has noted that a uoldtish dying in salt water lost aliout one-tifteeiith of 

 its weight, if the specimen were a small one. The loss was insignificant, on the other 

 hand, if the fish weighed several hundred grams. These fishes died, on tiic 

 average, in an hour's time, a period not long enough to permit of anj- extensive los>. 

 just as no considerable gain was found to occur in the case of the scup dying in 

 fresh water (experiments 69-71), above. Loaches and young eels, according to Beit, 

 lost one-tenth or even one-sixth of their weight; but both of these fishes have a naked 

 skin. In all of Bert's experiments the results of the changes were fatal, and the 

 phenomena were hence pathological. 



Fredericq (1904) records that the blood plasma of elasniobranchs increases in 

 volume in more dilute sea water, decreasing in less dihite. Of course a gain or l<)s> 

 of weight would be entailed thereby. According to Fredericq. however, the con- 

 ditions which obtain in sharks relative to osmosis are radically different from those 

 which hold for the teleosts. 



Various authors have described weight changes, due to osmosis, in the case of inver- 

 tebrates, but these need not be considered here. 



fHANCES OF WEKiHT IN DKAD FISHES. 



It has been noted that many of the tishes used in the foregoing set of experi- 

 ments died from the effect of the change of medium, and it likewise appears from 

 the records that in those cases in which death occurred the gain or loss was usually 

 much greater in a given time than in those cases where no harmful effects were 

 apparent. Compare, for example, experiment 81 or -41 h with 41 h' ; also experiment 

 41 e with experiment 8C." The catdsh in experiment 49 lost over 8 per cent of their 

 weight in 17 hours (probably 10 to 12 per cent in 1 day) and ultimately died, while 

 the white perch (experiment 51) lost 4.7 per cent and the salmon (experiment 55 <(] 

 only 3.1 per cent in a day in water of somewhat greater density, these two specio> 

 not being iiarmfully affected by the change. It is only fair to add, however, that in 

 the case of the rudd (experiment 50), which died after transfer to salt water, a loss of 

 only 4 per cent is recorded. This ma}' be due, it is true, to a subsequent gain through 

 imbibition of water after death (see below). 



I had at first supposed that the determination of a solution which was isotonic 

 with the body fluids of a given species of lish could l)e made simply enough by 

 immersing dead specimens in water of various degrees of salinity and noting the 

 effects upon their weight. A solution in which the weight remained stationary wotild 

 be isotonic. As a matter of fact, however, some species were found to increase in 

 weight in water of any specific gravity which was employed. 

 E.,:iHrhn,:ut 77." 



New York. Ai)ril. l'."05. The chinook salmon ( Oncorhynchus tschmryhcha).'' 

 the suntish {Etqjoinot!i< gihhosun)^ and the carp {Cyprinus carpid) among the 



a See pp. 73-74 for weight changes undergone by fishes used in experiments 81 and 86. They are not recorded in n<nr^ 

 for those experiments. 



ftThc snlmon is here counted among the fresh-water species because the earlier months of its life are passed in fresh 

 water and those specimens here used were taken from fresh w'ater. 



