KANWISHER, LAWSON. and SUNDNES: ACOUSTIC TELEMETRY FROM FISH 



peatedly handled for blood samples and had 

 largely accommodated to the presence of people. 

 Its heart slowed only when the fish was physi- 

 cally touched. 



At one point we started toward the fish with a 

 dip net. This was one which the fish had never 

 seen. It stopped swimming, faced the approaching 

 strange net, and extended its fins in what we had 

 come to recognize as a fright response. Its heart 

 stopped for 19 s. 



We detail these because we feel that such 

 acoustic telemetry will be a valuable adjunct to 

 behavior and sensory studies. When we have 

 monitored three fish simultaneously some ele- 

 ments of social interaction showed in their vari- 

 able heart rate. In particular, competition for 

 food was easily discerned after a few simultane- 

 ous observations of feeding and listening to the 

 EKG. In this manner we hope to build up a be- 

 havioral repertoire which will allow us to inter- 

 pret data from a fish swimming free in the ocean 

 where it cannot be observed. 



The potential effect of behavior on such 

 physiology as oxygen consumption had been pre- 

 viously shown by erratic increases when a fish 

 was confined in a respirometer (Sundnes, 1957a, 

 b). This could be overcome by keeping cod in a 

 laboratory aquarium for many weeks, while it 

 became used to people and capture. Veteran fish 

 were found to increase their O2 consumption and 

 also showed immediate color changes whenever 

 strangers were in the laboratory. We were reluc- 

 tant to accept the respiratory data until substan- 

 tiated by simultaneous observations of cardiac 

 response. 



Some species are difficult to acclimate to cap- 

 tivity. Atlantic salmon were brought directly 

 from a fish farm and wired for EKG transmitting. 

 They swam for several weeks at the maximum 

 sustainable speed until they died. From this we 

 could only learn the maximum heart rate. A 5-kg 

 salmon showed 60 to 62 beats/min. 



Later we have had fish which were hand fed in 

 a laboratory tank for over a year. When these fish 

 were tagged they were immediately returned to 

 familiar surroundings. They soon joined in feed- 

 ing frenzy and showed cardiac arrest when 

 frightened. When they were chased the heart 

 rate quickly increased, as shown in Figure 2. Rest- 

 ing rates below 30 beats/min were common. 



This approach was not successful with skipjack 

 tuna, Katsuwonus pelamis, in Hawaii. These 



2.5 K 

 SENSITIVITY 



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 5 



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HEARTBEAT TRANSMITTER 



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 CAPACITORS DECIMAL VALUES 



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WHOLE NUMBERS 



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Figure 5. — Simple beat frequency oscillator receiver. 



fast, probably warm-blooded fish were able to 

 either get rid of our transmitter, or died in the 

 effort. Their heart rates, however, were from 80 

 to 240 beats/min. This reflects their near mam- 

 mallike metabolic rate. They recovered from 

 fatigue in less than 1 h, much like man. We have 

 used a new miniature tag (7 mm diameter x 35 

 mm long) successfully on mackerel, Scomber 

 japonicus. 



CONCLUSIONS 



We have tried to outline the possibilities and 

 methods of acoustic telemetry from fish. It is a 

 valuable adjunct in both laboratory and open 

 water studies. In many cases, such as monitoring 

 the body temperatures of a free-swimming tuna, 

 it is the only way to get the desired data (Carey 

 and Lawson, 1973). The burgeoning solid state 

 technology promises a rapid advancement in 

 methodology beyond the relatively simple ele- 

 ments we have presented here. 



LITERATURE CITED 



Carey, F. G., and K. D. Lawson. 



1973 Temperature regulation in free-swimming bluefin 

 tuna. Comp. Biochem. Physiol. 44A:375-392. 

 Sundnes, G. 



1957a. On the transport of live cod and coalfish. J. Cons. 



22:191-196. 

 1957b. Notes on the energy metabolism of the cod (Gadus 

 callarias L.) and the coalfish (Gadus virens L.) in relation to 

 body size. Fiskeridir. Skr. Ser. Havunders. 11(9), 10 p. 

 Wardle, C. S.. and J. W. Kanwisher. 



In press. The significance of heart rate in free swimming 

 cod. J. Mar. Physiol. Behav. 



255 



