170 
PACIFIC SCIENCE, VoL XVII, April 1963 
hand it is tempting to postulate that the sub- 
stance is some metabolite which is released 
from gill, vent, or skin by excitement rather 
than by injury of the prey. 
Whatever may be the source and nature of 
the attractant, we have presented evidence that 
olfaction is involved in the predation of sharks 
on normal, healthy fish. It is suggested that in 
the natural environment, fish give off odors to 
which the sharks are conditioned. It is further 
suggested that when the fish become frightened 
or excited, and certainly if they rub against each 
other or against a coral head, they give off ad- 
ditional or new odors which stimulate the hunt- 
ing response in sharks. This hypothesis is con- 
sistent not only with our experimental data but 
also with our observations of the behavior of 
the sharks in their natural environment. For 
the most part they display a complete disregard 
for the myriad of normal, healthy fish which 
surround them. However they are able to track 
down and converge on a distressed fish (such 
as a live fish suspended from a hook through 
the jawbone but otherwise uninjured) with un- 
canny speed and accuracy. 
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