TOSHIAKI J. HARA
102
2. BARBELS OF CATFISH
Barbels play an important role in food taking in catfish. Application
of taste substances induced a train of spikes in the facial nerves innervating the nasal barbels of the catfish, Ameiurus melas (Tateda, 1961). By
stimulating with equivalent molar concentration of various chlorides,
the order of magnitude of responses was KC1 > NH,C1 > NaCl > Lick
thresholds for these salts were about 0.1 M . Solutions of NaC1, NaN03,
NaBr, and Na,-citrate in equivalent normal concentration elicited responses of similar amplitude. Hydrochloric acid induced a large initial
burst of impulses, which declined rapidly in 10-20 sec, at concentrations
of 0.0005-0.001 hl. Taste responses of isolated barbels of the catfish,
Parasilurus asotus, were also analyzed by recording potential discharges
from single nerve fibers (Tateda, 1964). The majority of single fibers
responded well to hydrochloric acid and salt but not to sucrose and
quinine. No simple classification of the taste fibers could be obtained. In
this connection, it must be pointed out that one single taste fiber may
innervate several taste receptor cells of different natures. Treatment with
KC1 and CaC12, although in themselves stimulating, caused a depressive
effect on the receptors and resulted in irreversible changes in the taste
responses at higher concentrations of 0.25-1.0 M . By short application of
urethane ( 13% for 20 sec) and cocaine (0.25% for 30 sec), taste responses
of the barbels to HC1 and NH,Cl were reversibly abolished. Furthermore,
from the analysis of stimulating effects of hydrochloric acid and several
organic acids (formic, acetic, propionic, and butyric) on the catfish barbels, it was shown that the responses to organic acids were greater than
those to hydrochloric acid at an equal hydrogen ion concentration and
that the responses increased with increase in molecular size of acids
tested (Tateda, 1966).
In sea catfish Plotosus anguillaris single taste fibers, responsive to both
NaCl and quinine, were most commonly found (Konishi et al., 1966).
Sucrose did not produce any appreciable response. It is surprising that
distilled water gave no positive response in most fibers despite the fact
that the receptors were rinsed with seawater between applications of
test solutions. Many fibers specifically responded to natural gustatory
substances such as extract of a marine worm and blood sera of other
animals. The active components of these stimulants are not yet known.
Electrical response to cysteine of the taste fibers of the barbels of
yellow bullhead ( Ictalurus natalis) was demonstrated to be impaired
after exposure to low concentrations (0.5 ppm) of detergents. Histological
examination revealed erosion of the taste buds. Affected fish did not fully
recover after 6 weeks in detergent-free water (Bardach et al., 196.5).
Recently, Mann (1969) reported that the deposition of phenolic sub-
102
2. BARBELS OF CATFISH
Barbels play an important role in food taking in catfish. Application
of taste substances induced a train of spikes in the facial nerves innervating the nasal barbels of the catfish, Ameiurus melas (Tateda, 1961). By
stimulating with equivalent molar concentration of various chlorides,
the order of magnitude of responses was KC1 > NH,C1 > NaCl > Lick
thresholds for these salts were about 0.1 M . Solutions of NaC1, NaN03,
NaBr, and Na,-citrate in equivalent normal concentration elicited responses of similar amplitude. Hydrochloric acid induced a large initial
burst of impulses, which declined rapidly in 10-20 sec, at concentrations
of 0.0005-0.001 hl. Taste responses of isolated barbels of the catfish,
Parasilurus asotus, were also analyzed by recording potential discharges
from single nerve fibers (Tateda, 1964). The majority of single fibers
responded well to hydrochloric acid and salt but not to sucrose and
quinine. No simple classification of the taste fibers could be obtained. In
this connection, it must be pointed out that one single taste fiber may
innervate several taste receptor cells of different natures. Treatment with
KC1 and CaC12, although in themselves stimulating, caused a depressive
effect on the receptors and resulted in irreversible changes in the taste
responses at higher concentrations of 0.25-1.0 M . By short application of
urethane ( 13% for 20 sec) and cocaine (0.25% for 30 sec), taste responses
of the barbels to HC1 and NH,Cl were reversibly abolished. Furthermore,
from the analysis of stimulating effects of hydrochloric acid and several
organic acids (formic, acetic, propionic, and butyric) on the catfish barbels, it was shown that the responses to organic acids were greater than
those to hydrochloric acid at an equal hydrogen ion concentration and
that the responses increased with increase in molecular size of acids
tested (Tateda, 1966).
In sea catfish Plotosus anguillaris single taste fibers, responsive to both
NaCl and quinine, were most commonly found (Konishi et al., 1966).
Sucrose did not produce any appreciable response. It is surprising that
distilled water gave no positive response in most fibers despite the fact
that the receptors were rinsed with seawater between applications of
test solutions. Many fibers specifically responded to natural gustatory
substances such as extract of a marine worm and blood sera of other
animals. The active components of these stimulants are not yet known.
Electrical response to cysteine of the taste fibers of the barbels of
yellow bullhead ( Ictalurus natalis) was demonstrated to be impaired
after exposure to low concentrations (0.5 ppm) of detergents. Histological
examination revealed erosion of the taste buds. Affected fish did not fully
recover after 6 weeks in detergent-free water (Bardach et al., 196.5).
Recently, Mann (1969) reported that the deposition of phenolic sub-