4. CHEMORECEPTION
103
stances and oils, released from aqueous flora, and their impairing effect
on taste and smell in carp was intensified by the presence of detergents
in water.
3. MODIFIED FINS AND OTHER FORMS OF MARINE FISHES
It is important to ascertain whether or not there are differences between external and oral chemoreceptors and to compare the taste sense
of marine and freshwater fishes. A series of observations have been carried
out with appendages of several species: (1) those whose barbels have
cranial innervation only (bullheads, lctalurus) , ( 2 ) those in which fins
have both cranial and spinal innervation ( tomcods, Microgadus tomcod),
and ( 3 ) those with modified fins innervated only by spinal nerves (sea
robins, Prionotus carolinus) (Bardach and Case, 1965; Fujiya and Bardach, 1966; Bardach et al., 196713). Acetic acid produced responses in
most nerve fibers of the barbel of the bullhead at a concentration of
0.0008 M , while in tomcod and sea robin about ten times the concentration was needed to evoke a response. This, however, does not imply that
marine fishes are less sensitive to acids; on the contrary, it means that
marine fishes are less able than freshwater fishes to perceive acids at the
same concentrations. Responses to acids depend on the presence of free
hydrogen ions in the solutions, and the above two acid solutions produce
about the same amount of hydrogen ions.
Upon application of NaCI, nerve discharges from both marine and
freshwater fishes increased only at concentrations higher than those of
their natural ecvironments. Reduction of nerve discharges in tomcods
and sea robins was observed at concentrations between 0.4 and 0.3 M
NaCl. Complete inhibition occurred when freshwater was applied; this
was followed by a transient augmentation of nerve discharges. Responses
to choline-chloride were similar to those to NaCl in three species. Varying
numbers of fibers responded to quinine hydrochloride. Only a few fibers
(less than 10%) responded to sucrose, and no response was observed in
sea robins where the fins have not taste buds but only spinal nerve
endings.
All three preparations responded well to flesh extracts. An attempt
has been made to extract the active component. Of various amino acids
which were identified in the extracts, only cysteine elicited strong responses; some of the fibers responded selectively only to cysteine. More
precise investigation will be required to resolve a question as to whether
or not there are taste qualities other than the four basic ones in fishes.
Katsuki et al. ( 1969) studied electrophysiological response to chemical
stimulation of pit organs of the nurse shark, Ginglymostoma cirratum.
103
stances and oils, released from aqueous flora, and their impairing effect
on taste and smell in carp was intensified by the presence of detergents
in water.
3. MODIFIED FINS AND OTHER FORMS OF MARINE FISHES
It is important to ascertain whether or not there are differences between external and oral chemoreceptors and to compare the taste sense
of marine and freshwater fishes. A series of observations have been carried
out with appendages of several species: (1) those whose barbels have
cranial innervation only (bullheads, lctalurus) , ( 2 ) those in which fins
have both cranial and spinal innervation ( tomcods, Microgadus tomcod),
and ( 3 ) those with modified fins innervated only by spinal nerves (sea
robins, Prionotus carolinus) (Bardach and Case, 1965; Fujiya and Bardach, 1966; Bardach et al., 196713). Acetic acid produced responses in
most nerve fibers of the barbel of the bullhead at a concentration of
0.0008 M , while in tomcod and sea robin about ten times the concentration was needed to evoke a response. This, however, does not imply that
marine fishes are less sensitive to acids; on the contrary, it means that
marine fishes are less able than freshwater fishes to perceive acids at the
same concentrations. Responses to acids depend on the presence of free
hydrogen ions in the solutions, and the above two acid solutions produce
about the same amount of hydrogen ions.
Upon application of NaCI, nerve discharges from both marine and
freshwater fishes increased only at concentrations higher than those of
their natural ecvironments. Reduction of nerve discharges in tomcods
and sea robins was observed at concentrations between 0.4 and 0.3 M
NaCl. Complete inhibition occurred when freshwater was applied; this
was followed by a transient augmentation of nerve discharges. Responses
to choline-chloride were similar to those to NaCl in three species. Varying
numbers of fibers responded to quinine hydrochloride. Only a few fibers
(less than 10%) responded to sucrose, and no response was observed in
sea robins where the fins have not taste buds but only spinal nerve
endings.
All three preparations responded well to flesh extracts. An attempt
has been made to extract the active component. Of various amino acids
which were identified in the extracts, only cysteine elicited strong responses; some of the fibers responded selectively only to cysteine. More
precise investigation will be required to resolve a question as to whether
or not there are taste qualities other than the four basic ones in fishes.
Katsuki et al. ( 1969) studied electrophysiological response to chemical
stimulation of pit organs of the nurse shark, Ginglymostoma cirratum.