It has been found that the captive tunny respond with a vigorous feeding 

 reaction to extracts of "food" substances such as skipjack and other fish (flesh* 

 viscera, blood), squid, and shrimp* The response to these several substances was 

 obtained regardless of which one was being fed to the fish as a subsistence diet. 

 However, there was an Indication of a slightly better response to a particular ex- 

 tract when the substtmce from which It was prepared was being used as food. This 

 observation, together with the fact that the fish were being fed on dead, out-op 

 materials, suggested that the captive fish may have learned to associate the smell 

 of the Juices exuding from the cut-up food with the act of feeding and that the 

 response to extracts was entirely conditioned by the nature of the food* This 

 would presume that the so-called "attractant" in the extracts is a substance (or 

 substances) common to the body Juices of fish, squid, shrimp, and other forms. As 

 the captive tunny will not forage for live bait occurring in the pond, but rather 

 oust be hand-fed, it is unlikely that further information on the question of con- 

 ditioning can be obtained from pond experiments* 



It was hoped that even if there was a partial conditioning of the pond 

 fish, tuna In their natural environment might be naturally "conditioned" to asso- 

 ciate the smell of living Injured or imlnjured prey with the act of feeding, and 

 that they would therefore respond to the extracts. This hope was not realized, A 

 sufficient nunber of sea tests on skipjack schools were conducted to warrant the 

 conclusion that the fish shewed no appreciable response to extracts of skipjack 

 flesh and viscera, extracts of yellowfin flesh, and extracts of live bait* Un- 

 fortunately no tests were conducted on "puj*e" schools of little tunny (the species 

 tested in the pond) or yellowfin (which are known not only to eat dead bait on 

 longlines but to respond occasionally to chumming with cut bait). Also, no sea 

 tests were conducted with extracts of squid and shrimp, both of which might be 

 considered a more natural food than skipjack or yellowfin flesh. Nevertheless the 

 negative results obtained from such sea tests as have been conducted indicate that 

 the sense of smell plays little part in the feeding of tuna In their natural en- 

 vironment* 



A study was made of the response of tuna at sea to a variety of inedible 

 luires which were used as chum, both with and without extract, after the fish had 

 been initially chummed to the stem of the ship with live bait* There was a momen- 

 tary response to shiny objects such as strips of tin, to silvery objeots such as 

 squares of aluminum foil, and to effervescing objeots such as calcium carbide 

 pellets* Similarly there was a momentary response to dead baitfish* The addition 

 of extract had no apparent effect. These results indicate that the sense of 

 vision plays a much greater role in feeding than the sense of smell* However* 

 neither these visual lures nor a "drag-lure array" (designed to simulate a school 

 of live bait) towed behind the vessel was successful in holding the fish at the 

 stem* 



The captive tunny in the pond were used to test a variety of edible lures 

 in whioh the qualities of visual attractiveness and palatabillty were combined. 

 Gelatin capsules, pieces of macaroni, and strips of agar treated with concentrated 

 extract ware eaten more frequently than when they were not treated with extract. 

 In some of the edible lures, visual attractiveness was increased by coating or im- 

 pregnating with aluminum powder. In a series of experiments in which the captive 

 tuna were presented alternately with maoaroad. pieces and agar strips, both cooked 

 in concentrated exti>aot and made silvery with aluminum, the fish shoved a prefer- 

 ence for the agar* The preference may have been associated with the texture of 

 the material. It became more pronounced with successive testing, s\iggestlng that 

 a learning process was Involved. 



Sea tests with these edible lures gave negative or Inconclusive results* 

 Unfortttnately the tests were made during the autumn, when skipjack schools were 

 both scarce and erratic in their behavior. Several of the schools whioh failed to 

 respond to the edible lures also failed to respond to live bait* The experiments 

 with the more promising substances (particularly with agar str'ps impregnated with 

 concentrated extract and alximlnum powder) should be repeated diwing the regular 

 summer skipjack season* If they again fail to attract our local skipjack schools, 

 which are notoriously difficult to chum with live bait, it does not necessarily 

 follow that they will also fail to attract skipjack, yellowfin, or other tuna 

 species elsewhere* 



19 



