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TosHLAgI J. HARA
chemoreception in fishes have followed two principal directions: (1) the
investigation of ecuity and range of the chemical sense organs, and ( 2 )
the investigation of the biological signifkance of chemoreception in the
behavior and life cycles of fishes. Chemoreceptive functions in fishes have
been well reviewed by Hasler (1957), Teichmann (1962b), and by
Kleerekoper (1969). During the last decade there has been a marked
increase in the number of studies dealing with the chemical sense in
fishes. Electron microscopy has been applied to the fine structure of the
chemoreceptor organs; recent electrophysiological investigations of the
chemosensory system have added greatly to the understanding of the
mechanism underlying chemoreception in fishes.
Chemoreception by animals shows a wide range of sensitivities. On
the basis of location and structure as well as the central innervation,
chemical reception has been divided into three categories: olfaction or
smell, gustation or taste, and common or general chemical sense. These
sensory modalities overlap somewhat: Some substances elicit responses
from both types of receptors. Practically, in terrestrial animals, those receptors which have high sensitivity and specificity, and which are “distance chemical receptors” are distinguished as olfactory, those receptors
of moderate sensitivity and stimulated by dilute solutions are gustatory
or “contact chemical receptors,” and those receptors which are relatively
insensitive and nondiscriminating are considered common chemical sense.
In fishes, smell and taste are both mediated by dilute aqueous solutions
so that the distinction is made anatomically and physiologically.
Olfactory organs are innervated by the &st cranial nerve which contains the axonal extensions of the primary receptor cells to the olfactory
bulb. Through the olfactory tracts bulbar activity is related to the rest
of the nervous system. Those fishes with well-developed olfactory capacities are called “macrosmatic”; those in which the capacities are less acute
are called “microsmatic.”
Taste is mediated through the taste buds with the secondary sensory
cells. Taste buds lie not only in the mouth and pharynx but also in the
gill cavity, on the gill arches, on appendages such as barbels and fins,
and also, in some fishes, on all external surfaces of the body. The taste
buds are innervated by the VIIth, IXth, and Xth cranial nerves which
terminate in much enlarged vagal lobes.
Common chemical sense, which was originally named by Parker
(1912), is also located on exposed body surfaces of fishes. These are free
nerve endings supplied by the spinal nerves. In contrast to the two senses
mentioned above, the general chemical sense is relatively low in
sensitivity.
TosHLAgI J. HARA
chemoreception in fishes have followed two principal directions: (1) the
investigation of ecuity and range of the chemical sense organs, and ( 2 )
the investigation of the biological signifkance of chemoreception in the
behavior and life cycles of fishes. Chemoreceptive functions in fishes have
been well reviewed by Hasler (1957), Teichmann (1962b), and by
Kleerekoper (1969). During the last decade there has been a marked
increase in the number of studies dealing with the chemical sense in
fishes. Electron microscopy has been applied to the fine structure of the
chemoreceptor organs; recent electrophysiological investigations of the
chemosensory system have added greatly to the understanding of the
mechanism underlying chemoreception in fishes.
Chemoreception by animals shows a wide range of sensitivities. On
the basis of location and structure as well as the central innervation,
chemical reception has been divided into three categories: olfaction or
smell, gustation or taste, and common or general chemical sense. These
sensory modalities overlap somewhat: Some substances elicit responses
from both types of receptors. Practically, in terrestrial animals, those receptors which have high sensitivity and specificity, and which are “distance chemical receptors” are distinguished as olfactory, those receptors
of moderate sensitivity and stimulated by dilute solutions are gustatory
or “contact chemical receptors,” and those receptors which are relatively
insensitive and nondiscriminating are considered common chemical sense.
In fishes, smell and taste are both mediated by dilute aqueous solutions
so that the distinction is made anatomically and physiologically.
Olfactory organs are innervated by the &st cranial nerve which contains the axonal extensions of the primary receptor cells to the olfactory
bulb. Through the olfactory tracts bulbar activity is related to the rest
of the nervous system. Those fishes with well-developed olfactory capacities are called “macrosmatic”; those in which the capacities are less acute
are called “microsmatic.”
Taste is mediated through the taste buds with the secondary sensory
cells. Taste buds lie not only in the mouth and pharynx but also in the
gill cavity, on the gill arches, on appendages such as barbels and fins,
and also, in some fishes, on all external surfaces of the body. The taste
buds are innervated by the VIIth, IXth, and Xth cranial nerves which
terminate in much enlarged vagal lobes.
Common chemical sense, which was originally named by Parker
(1912), is also located on exposed body surfaces of fishes. These are free
nerve endings supplied by the spinal nerves. In contrast to the two senses
mentioned above, the general chemical sense is relatively low in
sensitivity.