of the tanko After the cloud had diffused until it was barely visi- 

 ble, the tuna eventually entered ito With the stronger solutions 

 it took a proportionately longer period of time for the tuna to re- 

 turn to the down-stream part of the tanko Apparently there is a 

 critical concentration above which there is a repellent effect,, 

 This J howe%'"er5 is not too marked as in one experiment (the only one 

 with this reaction) both the yellowfm aiid the tunny swam right 

 through the cloud (Oel percent, or weakest solution) from the start 

 of siphoningo Despite this instance, it may be concluded that cop- 

 per acetate solution has a repellent effect on tuniy although its 

 action is not as pronounced as in the case of manini and baitfisho 



DISCUSSION AND CONCLUSIONS 



As the tuna are predacious fish, it might be expected that the 

 most important sense involved in feeding would be the eyesight, fol- 

 lowed perhaps by hearing o However other sense 3 ^ as for example the 

 chemical sense in its widest meaning^ cannot be excluded on an a 

 priori basis o The experiments reported in this paper show that~a 

 chemical sense is present, and this in&cates that it may play some 

 part in feedingo It is impossible to say whether the chemical sense 

 is smell or taste or^ in other words, whether sense organs in the 

 mouth or the nose are being stimulatedo However j, both senses are 

 usually well-developed in fish as other investigators of fresh- 

 water and marine fishes have shown (Adrian and Ludwig I9385 Berghe 

 1929j Copeland 1912, von Frisch 19l|l> Greene 1925, gEz 19hl, Hasler 

 and V/isby 19U9| Huttel 19kli Klenk 1930| Naurath 19U9; Par-ker 1910. 

 1911, 1913, 1922| Scharrer, Staith, and Palay 19k7j Sheldon 1911? 

 Strick 192i+, 1925| Trudel 1929, Walker and Hasler 19ii9^ Wrede 1932) c 



The experiments of g8z (I9i4.1) and Wred© (1932) showed that the 

 skin of fish secretes a substance which can be perceived chemically 

 not only by fish of the same species but also by fish of other spe- 

 cies, and that the substance could be recognized by smell o It was 

 thought that the same might be true for tuna^, ioCo, that they could 

 smell the presence of other fishes^ However, this was not the case, 

 as shown by the negative eaqjeriments with "conditioned" water in 

 which baitfish had been livingo 



Von Frisch (19Ul) found that the skin of injured minnows 

 ( Phoxinus laevis) gives off odoriferous substances, probably purin- 

 or pterin-like which cause alarm reactions in the same and related 

 species o It was thought that an alarm or repellent stimulus to the 

 prey might be an attractant stimulus to tte predator,, ioeo, that 

 baitfish or squid preparations might attract the tunao The experi- 

 ments reported here brought quite unexpected results to lights the 

 tuna reacted not at all, or only weakly,, to extracts of squid (a nor- 

 mal foodO and of baitfish (a food which they will take when thrown 



31 



