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TASTE FUNCTIONS IN FISH 



JiHEi KoNiSHi and Yngve Zotterman 



Laboratory of Physiology and Ecology, Faculty of Fisheries, Prefectural 

 University of Mie, Tsu, Japan and the Department of Physiology, Kungl. 

 Veterinarhogskolan, Stockholm, Sweden. 



This paper deals with the electric activity of gustatory fibres of freshwater 

 fish and especially with the problem of specific receptors responding to 

 substances which may attract fish. 



Hoagland (1933) was the first to record nerve discharges from gustatory 

 fibres in the facial nerve which innervate the barbels of the catfish. He 

 showed that chemicals initiate nerve impulses that are of smaller spike 

 height than those produced by mechanical stimulation. Recently we found 

 that the barbels are much less sensitive to chemical than to mechanical 

 stimulation (Konishi and Zotterman, 1961). In the roof of the carp's 

 mouth particularly dense taste buds are found. This palatal organ is 

 supplied by nerve fibres from the palatine nerve. Responses led from the 

 nerve evoked by the application of sapid substances were found to be very 

 strong. Besides chemoceptive and motor fibres the palatine nerves con- 

 tain fibres which respond very selectively to mechanical stimulation. The 

 integrated response to touch is, generally, much smaller than that to 

 chemical stimulation. 



The palatine nerves in Swedish carp responded to all four conventional 

 classes of taste substances such as salt, sucrose, quinine and acid — especi- 

 ally strongly to acid (0.005 M/pH 3.8/acetic acid) and sucrose (0.5 m), and 

 weakly to quinine (0.01 m) (Fig. 1). Water did not stimulate the chemo- 

 ceptors of this fish, after a previous rinse with water. The low sensitivity 

 offish to quinine is in close agreement with Trudel's behavioural results on 

 minnows (1929). Generally, quinine receptors adapted very quickly with 

 repeated application, whereas the others did not. h\ all the nerve pre- 

 parations tested, glycol and glycerol (which taste sweet to humans) elicited 

 a positive response, while saccharine gave a very feeble response if any. It 

 is of particular interest that human saliva had a strong stimulating eff'ect 

 on the chemoceptors, and gave a much larger integrated response than the 

 0.5 M NaCl solution. Earthworm and milk also produced massive res- 

 ponses. The responses to sapid substances in Japanese carp were found to 

 be different from European, as shown in Fig. 2. Response to sucrose 

 (0.5 m) was always quite small, while quinine (0.01 m) gave a much larger 



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