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to the observer sitting in the cage as it obviously 
was to the sharks. 
Recalling some of the observations made 
earlier, we might consider again the speared 
grouper which rested motionless on the bottom 
while 12 sharks swam slowly about in its im- 
mediate area. Although this grouper was in 
a completely exposed position, its coloration 
blended in well with the bottom on which it 
was resting. In this position the grouper was 
apparently at least temporarily safe from attack 
by the 12 sharks, in spite of the fact that it was 
wounded and still emitting the olfactory stim- 
ulus which presumably had released the ap- 
petitive behavior pattern which these sharks 
were at that time demonstrating. At Engebi, the 
sharks struck at the rock which was sitting in 
the middle of the sandy area, floating seaweed, 
and the lead weight — all inanimate objects in 
the immediate area of the bait, but all of which 
sharply contrasted in brightness with the back- 
grounds against which they were viewed by the 
sharks. These results are consistent with the con- 
clusions drawn by Gilbert (1961) from ana- 
tomical studies of the shark eye. 
Although there is little doubt that vision is 
the predominant directing sense within the 
visual field, the effective distance involved here 
will be highly variable. Such external factors as 
water clarity, incident light, and whether or not 
the prey is under cover, no doubt determine the 
effectiveness of vision in any given situation. 
RESPONSE TO GUSTATORY AND 
TACTILE STIMULI 
While lack of visual discrimination appar- 
ently led to selection of the wood as often as it 
did the fish during Experiment VIII, the shark 
was quick to learn its error. Initially the wood 
was actually taken into the mouth, but after 
one or two successive trials a nudge was gen- 
erally sufficient to dismiss the inedible object. 
An appraisal of the bait by the visual or olfac- 
tory sense may have been the basis for the 
nudge, but when the bait was taken into the 
mouth, other senses, e.g., gustation and/or tac- 
tile sense, undoubtedly came into play. 
A review of the gustatory sense of sharks is 
presented by Tester (ms). In this review, he 
points out that while the receptors of the gus- 
PACIFIC SCIENCE, Vol. XVII, April 1963 
tatory sense (e.g., taste buds or terminal buds) 
occur in the skin of the body, fins, and barbels 
of many species of fishes, in the elasmobranchs 
they appear to be associated with papillae which 
are confined to the epithelial lining of the 
mouth and pharnyx. He also calls attention to 
the claim of Budker (1938) that the "pit or- 
gans" located on the body of elasmobranchs have 
a gustatory function. 
An effort was made to design an experiment 
which would illustrate the respective roles 
played by both gustation and the tactile sense 
in accepting or rejecting food taken into the 
mouth. As the block of wood in Experiment 
VIII differed from the fresh fish in tactile cues 
as well as those of olfaction and gustation, it 
was impossible to say which of the two might 
have been more influential in the rejection of 
the wood. 
An attempt was made to synthesize a bait 
which possessed the visual and tactile properties 
of acceptable bait, but which lacked the olfac- 
tory and gustatory properties. Tester et al. 
( 1955) concluded that in the flesh of many 
fishes there is present a substance or substances 
which, when extracted with alcohol or water, 
can be perceived by a fish through its sense of 
smell or taste and which promotes the urge to 
feed. Tester commented (personal communica- 
tion) that extraction by alcohol was effective in 
removing this substance from a piece of flesh. 
He observed that squid prepared this way was 
not detected by blinded blacktips and although 
taken into the mouth by normal blacktips, they 
were subsequently rejected. He attributed this 
rejection to the lack of acceptable gustatory 
stimulation, in as much as the texture of the 
prepared squid seemed to be similar to untreated 
squid. 
The following experiment was an attempt to 
duplicate Tester’s results in the field. 
Experiment X 
This experiment was designed to determine 
whether or not a bait offering the visual and 
tactile stimuli of food, but which lacks the ol- 
factory or gustatory stimuli, will be acceptable 
as food by these sharks when they are actively 
feeding. 
A number of 3 -inch cubes of grouper flesh 
