4. CHEMORECEPTION
93
teristic behaviors such as circular and zigzag movements during which
the direction of the odor gradient might be searched. Changes of water
turbulence at the olfactory mucosa could help to overcome the adaptation
of the olfactory receptor cells. When amylacetate was applied instead
of coumarin, the fishes generally behaved in a positive way. Furthermore,
when coumarin and amylacetate were given simultaneously at the opposite sides of the fish tank, the fish preferred coumarin, to which they
were originally trained (primary differentiation).
B. Gustatory Sense
As mentioned above, the argument that taste is a different sensory
function from olfaction is based on the training of blinded minnows to
discriminate certain taste substances even after extirpation of the olfactory lobes, while conditioning for odorous substances was only possible
in intact fishes ( Strieck, 1924).
Trudel (1929) compared the sensitivity of the minnows for various
taste substances-especially saccharides and synthesized sweet substances.
Fructose, glucose, galactose, mannose, mannite, arabinose, maltose,
lactose, melezitose, raffinose, and two sweet substances, saccharin and
dulcin, were all perceived by the minnows as essentially the same quality
as sucrose. Trudel also reported that fructose was detected as the sweetest
of all and that the relative threshold of the minnows for quinine (as low
as 0.0025%) was higher than that of humans ( 0.003%).
Krinner (1935) was the first to provide accurate thresholds for sucrose
( 2 x
M ) in minnows using his careful training techniques. These thresholds were 512 and 184 times lower, respectively, than those of humans for sucrose and salt. Removal of olfactory
lobes caused no change in these thresholds, thus verifying that a true
gustatory sense was involved.
Recently, by developing Krinner's training technique, Glaser ( 1966 )
has carefully compared taste sensitivity of the minnow Phoxinus plzoxinus,
stickleback Gasterosteus aculeatus, South American salmon Hemigrammus
caudovittatus, and Mexican blind cave fish Anoptichthys jordani. The
time necessary to learn their task for a given taste substance (e.g., sucrose)
differed greatly in various species; in Anoptichthys training was unsuccessful. Differences were also found within a species for various taste substances; for instance, minnows could be most easily trained for sucrose;
this was followed by acetic acid, sodium chloride, and quinine. Of four
basic taste substances, the reaction time for NaCl was longest in the
minnow and that for sucrose in Gasterosteus, Phoxinus, and HemigramM ) and salt ( 4 x
93
teristic behaviors such as circular and zigzag movements during which
the direction of the odor gradient might be searched. Changes of water
turbulence at the olfactory mucosa could help to overcome the adaptation
of the olfactory receptor cells. When amylacetate was applied instead
of coumarin, the fishes generally behaved in a positive way. Furthermore,
when coumarin and amylacetate were given simultaneously at the opposite sides of the fish tank, the fish preferred coumarin, to which they
were originally trained (primary differentiation).
B. Gustatory Sense
As mentioned above, the argument that taste is a different sensory
function from olfaction is based on the training of blinded minnows to
discriminate certain taste substances even after extirpation of the olfactory lobes, while conditioning for odorous substances was only possible
in intact fishes ( Strieck, 1924).
Trudel (1929) compared the sensitivity of the minnows for various
taste substances-especially saccharides and synthesized sweet substances.
Fructose, glucose, galactose, mannose, mannite, arabinose, maltose,
lactose, melezitose, raffinose, and two sweet substances, saccharin and
dulcin, were all perceived by the minnows as essentially the same quality
as sucrose. Trudel also reported that fructose was detected as the sweetest
of all and that the relative threshold of the minnows for quinine (as low
as 0.0025%) was higher than that of humans ( 0.003%).
Krinner (1935) was the first to provide accurate thresholds for sucrose
( 2 x
M ) in minnows using his careful training techniques. These thresholds were 512 and 184 times lower, respectively, than those of humans for sucrose and salt. Removal of olfactory
lobes caused no change in these thresholds, thus verifying that a true
gustatory sense was involved.
Recently, by developing Krinner's training technique, Glaser ( 1966 )
has carefully compared taste sensitivity of the minnow Phoxinus plzoxinus,
stickleback Gasterosteus aculeatus, South American salmon Hemigrammus
caudovittatus, and Mexican blind cave fish Anoptichthys jordani. The
time necessary to learn their task for a given taste substance (e.g., sucrose)
differed greatly in various species; in Anoptichthys training was unsuccessful. Differences were also found within a species for various taste substances; for instance, minnows could be most easily trained for sucrose;
this was followed by acetic acid, sodium chloride, and quinine. Of four
basic taste substances, the reaction time for NaCl was longest in the
minnow and that for sucrose in Gasterosteus, Phoxinus, and HemigramM ) and salt ( 4 x