THE AQUARIUM, JANUARY, 1897. 



85 



ter brackish water, where the tide ebbs 

 and flows, and live there a sufficient 

 time to habituate themselves to the 

 change. This accounts for the frequent 

 discovery of large numbers of such 

 migratory fish in the vicinity of the 

 mouths of the rivers which they ascend. 



A fresh water eel, plunged in salt 

 water, does not seem to be affected. 

 But in investigating the peculiarities of 

 this species, M. Bert was led into a 

 wrong conclusion, which may be cited 

 to show how easy it is, often by pure 

 accident, to reach an erroneous deter- 

 mination in laboratory experimenting. 

 After having himself placed several 

 fresh water eels in salt water, he found, 

 as already stated, that they remained 

 alive and unharmed. Wishing to con- 

 tinue the experiments, he directed his 

 assistant to introduce the fish and re- 

 port results. To his surprise, the eels 

 then persistently died after a three or 

 four hours' sojourn in salt water, and 

 long search failed to discover the reason 

 why it was that, when M. Bert placed 

 them in the tanks they lived, while 

 when his assistant did so, they perished. 

 Finally M. Bert found that his assistant, 

 doubtless on account of the slipperiness 

 of the eels, lifted them with a piece of 

 cloth in his hand. The cloth rubbed 

 off a little of the natural slime of the 

 animal, which protected them from salt 

 water. Osmosis then occurred in the 

 denuded portion, and the eel eventually 

 died. 



The converse experiment of inserting 

 sea fish in fresh water, produced analo- 

 gous results. The gills were the seat 

 of alterations, the same as those noted 

 in fresh water fish placed in salt water. 

 M. Bert also observed that the life of 

 the sea fish could be prolonged by add- 

 fng salt to the fresh water, thus adding 

 further confirmation to his theory. 



"THE HEARING OF A FISH. 



For an inquiry whether fishes have a 

 sense of hearing, Herr A. Kreidt exper- 

 imented upon goldfish — normal, fish 

 poisoned with strychnine, and fish de- 

 prived of their labyrinths. Sounds 

 were made by sonorous rods plunged in 

 the aquarium, to which tuning forks 

 or bows were applied out of the water. 

 Whistling and the ringing of bells out- 

 side of the water produced no impres- 

 sion on either of the three classes ex- 

 perimented upon. But all responded 

 whenever the apparatus within the 

 aquarium was struck with the produc- 

 tion of an audible sound. The conclu- 

 sion was drawn that fish do not hear as 

 in ordinary hearing with the ears, but 

 that they are sensitive to sonorous 

 waves which they can perceive through 

 some skin-sense." 



Respecting the above extract, I may 

 state that after a period of over thirty 

 years' observations on fish of almost all 

 kinds, in my private aquarium, I long 

 ago came to the conclusion that fish 

 have no perceptible hearing, in the or- 

 dinary sense of that term. The loud- 

 est noises made in the room in which 

 the aquarium stood, failed to excite 

 them in any way. They would remain 

 suspended in mid-aquarium, or swim- 

 ming around without the slightest re- 

 gard to the noises, or being in any way 

 disturbed thereat. But the slightest 

 shock to the stand on which the 

 aquarium was placed, or the slamming 

 of a door, or any motion by which the 

 aquarium itself would be disturbed, 

 had the effect of creating a fish panic. 

 The conclusion I arrived at is that vi- 

 bration acts on an aquarium's occu- 

 pants in the same way as sudden noise 

 acts on other animals, and that it is 

 through the sense of shock or vibration 



