EFFECTS OF EXPLOSIVE SOUNDS UPON FISHES. 7 



has grown to such an intensity as would have been effective had a 

 single shock been delivered at- once to the fish. The gradual ap- 

 proach of the boat, then, does away with the element of contrast 

 between silence and loud noise, and the result is just the reverse of 

 that of summation, so often seen in the application of minimal 

 stimuli to sense organs ; the fish fails to respond. 



RESPONSE TO THE SOUND OF GUNSHOTS. 



If this explanation of the general ineffectiveness of motor boats 

 in disturbing fishes is correct, then these animals ought to be re- 

 sponsive at least to single, loud noises generated close to the water. 

 As long ago as 1782 Hunter demonstrated that fishes were respon- 

 sive to the discharge of a fowling piece. In his account of the in- 

 ternal ears of fishes he states that — 



In the year 1762, when I was in Portugal, I observed in a nobleman's gar- 

 den near Lisbon a small fishpond, full of different kinds of fish. Its bottom 

 was level with the ground and was made by forming a bank all round. There 

 was a shrubbery close to it. Whilst I was lying on the bank, observing the 

 fish swim about, I desired a gentleman who was with me to take a loaded 

 gun and go behind the shrubs and fire it. The reason for going behind the 

 shrubs was that there might not be the least reflection of light. The instant 

 the report was made the fish appeared to be all of one mind, for they vanished 

 instantaneously into the mud at the bottom, raising as it were a cloud of mud. 

 In about five minutes after they began to appear, till the whole came forth 

 again. 



It is quite evident from this observation by Hunter that fishes 

 can be disturbed by the discharge of a gun in the air, even when it 

 is some distance from them. 



To test the effect of single, loud noises on fishes several Fundulus 

 were liberated in a cage, and after they had become quieted a fowl- 

 ing piece was discharged a few feet from them, but in such a posi- 

 tion that they could not see it. At the report of the gun most of 

 the fishes gave a single leap forward and to one side. This was 

 several times repeated at considerable intervals and invariably with 

 the same results. Bait was then thrown into the cage, and while 

 the Fundulus were busy tussling with this food the gun was again 

 discharged. They immediately forsook the bait, but in half a minute 

 they had returned to it with full vigor. From these tests it is evi- 

 dent that Fundulus is easily disturbed by such a noise in the air as 

 the discharge of a gun, but it is also evident that this disturbance 

 is of a very temporary kind. \ 



To ascertain something of the strength of the sound stimulus that 

 caused the Fundulus to react an observer dove under the water, and 

 while he was there the gun was discharged in much the same rela- 

 tion to him as it had been to the fishes. Although the report of 

 the gun in the air was almost deafening, when it was heard under 



9275°— 13 G 



