FISHERY BULLETIN: VOL. 72. NO. 2 





100 p( 



lOOpf 

 NPO 



150 fBj 



lOOpf 



2.2 mh 1_ 



1.4 V 



MALLORY 

 #RM 450 R 

 BATTERY 



T,— TRANSDUCER, PZT-4 CERAMIC CYLINDER 1.27cm O.D. 



1.02cm ID. 

 FREQUENCY = 50 kHz 1.41 cm LONG 



FREQUENCY DEVIATIONS 200 h; /mv^' EKG INPUT 



fatigue can result in an increased heart rate for 

 as long as 10 to 20 h while this debt is being 

 repaid. Thus one gets a substantiation of the 

 already recognized biochemical changes in mus- 

 cle glycogen and lactic acid. When remote 

 monitoring shows a rapid heart rate one cannot 

 tell if the fish is swimming at that moment or is 

 reflecting a previous exhaustion. 



Behavior 



Figure 3. — Small heart beat transmitter. 



teraction. At such times we could direct our at- 

 tention more intently. Generally we have found 

 that heart rate changes are related to specific de- 

 tails of a fish's physiology and also its behavior. 



The transmitter can usually be carried in the 

 stomach of the fish. It is readily inserted into an 

 animal which has been anaesthetized with 

 MS-222.3 The EKG lead is brought out under the 

 last gill arch. It is pushed under the skin im- 

 mediately over the heart. The receiving hyd- 

 rophone is placed against the fish so the trans- 

 mitter can be monitored. There is no difficulty in 

 interpreting when the lead placement for op- 

 timum EKG signal has been reached. The lead is 

 then sutured in place. 



The gills can now be flushed with anaesthetic- 

 free water and the fish soon released. The entire 

 operation takes 3 or 4 min. The fish will have 

 been under anaerobic stress because no water has 

 been flowing over the gills. Most specimens ap- 

 pear to fully recover in a few hours. 



If drag is not important the transmitter can be 

 sutured to the outside of the fish. This method 

 has allowed us to work with plaice, Pleuronectes 

 platessa, whose stomachs were too small. It was 

 also convenient for some Atlantic cod and Atlan- 

 tic salmon that repeatedly threw up a stomach 

 tag. 



Physiological Response 



When a fish is swimming we find an expected 

 increase in heart rate, reflecting the increased 

 oxygen transport of the cardiovascular system. 

 In an Atlantic cod this is a measure of both the 

 instantaneous exertion, and also of any previ- 

 ously incurred oxygen debt (Wardle and Kan- 

 wisher, In press). Chasing a fish to maximum 



We were not prepared for the large component 

 of behavioral response observed in the heart rate 

 of all fish. Cardiac arrest is a well known re- 

 sponse in conditioning. We found it to occur with 

 the subtlest of cues, once the fish had recovered 

 from initial handling. This can best be described 

 by two anecdotes. 



A plaice, which had not eaten for many 

 months, had settled into the sand on the bottom 

 of a 60-ft circular laboratory aquarium. It was 

 mid-winter with low water temperatures and the 

 fish appeared to be doing the equivalent of hiber- 

 nating. In spite of this outward lethargy it re- 

 sponded to doors opening, relays clicking, and to 

 any other sort of human activity in the vicinity. 



It was, not unexpectedly, most sensitive to vis- 

 ual cues. We gradually reduced these to smaller 

 objects moved in the visual field of the fish. The 

 most sensitive response came early in the morn- 

 ing before local laboratory activity had started. 

 At this time we could come quietly up to the tank 

 and push a pencil a few centimeters over the 

 edge. The plaice, \V2 m below responded by stop- 

 ping its heart for 8 or 9 s. 



Another incident concerned a venerable cod of 

 more than a year in captivity. It had been re- 



S 22K I 22K 



2N5813 

 „N 1200i iZOOie] n 



Q,' {k\%' ;k( — ° 



5| '0.11 ;i4 

 2 



 . 4.05 V 

 MALLORY 

 #TR 133R 

 BATTERY 



"■1.2 „f 



2N3663 J?- 



1 V'tL' 



SEMICONDUCTOR 

 PRESSURE TRANSDUCER 

 KULITE#T0S-360-25 



FAIRCHILD OP AMP 

 #110 776 



R SELECTED TO NULL OFFSETS IN A 



1 THERMISTOR. 2K^25°C 



T, AS USED IN LARGE HEARTBEAT 

 TRANSMITTER 



B CMOS BUFFER SOLID STATE SCIENTIFIC 

 jjf SCL4441AF 



FREQUENCY=«55 kH; 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Figure 4. — Pressure transmitter. 



254 



