KANWISHER, LAWSON, and SUNDNES: ACOUSTIC TELEMETRY FROM FISH 



ATLANTIC COD - GADUS MORHUA 



C D 



PR PR T P R 



T 



PR T P R 



1 SEC 



ATLANTIC "t^hV-UOV^- SALMO SALAR 



. 1 SEC . 



J,.^ i 



\ 1- 



j^ _Y-|-- — I — t^/^^l +- 



"h^^ 



V^~/-~- ^-ry-^- ^ |~Atj'^v_-^J^j^.^-^'^-^(sJ^,^^,Y — -'1.\\«vA\|\v^-4-,.\- 



• • • • • • 



Figure 2.— Examples of electrocardiogram from free swimming Atlantic cod and Atlantic salmon. The experimenter approached the 

 aquarium at A and looked over at B. slowing the heart rate. When he went away the heart started at the maximum rate at C, since the T wave 

 is piled on the next P wave at D. The Atlantic salmon also showed a slowing at E from the same source. It was chased at F, resulting in a 

 quickly accelerating heart rate from exercise. Noise while swimming is an acoustic artifact from reflections in the tank. 



ment has an operating life of 1 wk. We are using it 

 to study gas pressure in swim bladders. With a less 

 sensitive sensor we can determine pressures at 

 depths equal to 1,000 m. 



Receiver 



Much of our work has been done with tunable 

 superheterodyne receivers. These employ a 

 mechanical filter to set bandpass. Nearly equiv- 

 alent results can be had from the simpler circuit 

 of Figure 5. The hydrophone contains a frequency 

 selective preamplifer with a voltage gain of 100. 

 Amplification within the hydrophone is impor- 

 tant to eliminate interference from motor igni- 

 tion and radio stations. Power for this preamp- 

 lifer comes down the same wire that carries sig- 

 nals to the receiver. 



The preamplified signal is amplified another 

 100 times in Ai (}h of a 1437 dual operational 



amplifier). Its output is mixed with a local oscil- 

 lator in Q3 to produce a signal at the audio differ- 

 ence frequency. This is amplified 10 times in A2 

 and used to drive headphones. A l-fiv signal at 

 the receiving hydrophone is clearly audible. 



RESULTS 

 General 



We originally developed our telemetry so it 

 could be used with ease for human cardiac 

 monitoring. Work with fish only required 

 miniaturization. The usual method is to have the 

 receiver output played through a speaker in the 

 laboratory. This allows one to notice occasional 

 events of interest. Such more or less casual 

 monitoring has greatly reduced the need for ob- 

 servational patience. In this way we have ob- 

 tained cues related to feeding and behavioral in- 



253 



