PHYSIOLOGY OF CHEMORECEPTION 



Combined EEG /Behavioral Studies on Free-Swimming Sharks 



237 



The apparatus used for studies on free-swimming sharks is shown in Figure 4. 

 A 1150-gal. circular flow system was driven by propellers so that the sea- 

 water moved through a hydrodynamic tunnel at a uniform rate on all levels, 

 without appreciable turbulence. Chemicals introduced near the propellers 

 circulated in precisely known dilutions and time intervals, passing through 

 the glass observation chamber. 



After a brief period of acclimatization when first placed in the observation 

 chamber, sharks took up their regular unstimulated activity patterns within 

 the chamber. Lemon sharks swam continuously but slowly. Nurse sharks 

 settled on the bottom of the observation chamber, snouts directed upstream; 

 they rarely swam again until stimulated by a chemical test solution in the 

 water current. All sharks had electrodes implanted in several locations, 

 always including either the olfactory bulb or the anterior lateral area of the 

 telencephalon, as described in the previous section. Wires from the im- 

 planted electrodes led through a swivel, adjusted to allow complete free- 

 dom of motion, to the EEG recording apparatus. 



i 



Figure 4 Hydrodynamic tunnel for testing responses of free-swimming sharks to known 

 concentrations of pure chemical stimuli. Top of apparatus removed, showing channel for 

 nonturbulent flow of seawater. Glass observation tank on right, near observer. 



