the case of fatty or oily substances, by dispersing in water with a 

 dispersing agent "Tergitol". If the latter was not effective, the 

 mixture was forced through an emulsifying apparatus to insure its 

 complete dispersion. 



RESPONSE TO SIMPLE EXTRACTS OF TUNA AND OTHER FISH 



Flesh Extracts of Tuna 



There are nnany experinnents to show that in both the tank 

 ajid the pond the tunny (and to a lesser extent, the yellowfin) gave a 

 positive response to clear, aqueous extracts of skipjack flesh (Nos„ 1, 

 8, 10, 13, 20, 50, 54, 64, 65, 66, 67, 72, 80, 81, 82, 87, 93, 97, 

 106, 111, 112, 117, 118, 122, 128, 135, 173, 199, 207), yellowfin 

 flesh (Nos, 14, 18, 26), tunny flesh (No, 27) and bigeye flesh 

 (NoSo 239, 252, 259), To these might be added a large nxxnttber of ex- 

 periments using either water or alcohol for extraction in which the 

 materials were subjected to further treatment and which in many cases 

 gave a positive response. In only a few experiments with simple ex- 

 tracts were negative results obtained when positive results were 

 expected. In tank experiment No. 16, the fish had been fed 2 hours 

 previously and were not responsive to skipjack flesh extract. In tank 

 experiment No. 63 there was no response, due probably, as has been 

 mentioned previously, to the dulling produced by an accumulation of 

 test products in the tank with too frequent testing. In pond experiment 

 No. 336, the fish failed to enter the attraction area during the 15-minute 

 test period. In a few experiments, of course, the response was un- 

 certain or slight (X)„ 



The nature of JJie response to extracts of tuna flesh has 

 already been described. It is a complex reaction, consisting prima- 

 rily of an urge to feed, which is manifested by speeding, surfacing, 

 circling, snapping at objects, together with a return to the area of 

 stimulation. 



It is presumed that in tuna flesh there is present a 

 substance (or substances) which, when extracted and presented to the 

 tunny, can be perceived through the fish's sense of smell or taste. 

 The substance which, when smelled or tasted, promotes the urge to 

 feed is henceforth called the "attractant, " Unfortunately, as already 

 pointed out, the response varies greatly in strength or manifestation 

 between similar experiments. It appears to be influenced by many 

 uncontrolled and perhaps uncontrollable factors. 



One experiment (No. 112) is described in detail, for it 

 differed from the others in method and purpose. Three liters of stock 



30 



