4. CHEMORECEPTION
113
this fish is by spatial and temporal comparison of intensities, that speed
is related to the rate of change in stimulation, and that variation in turning serves to maintain fish at high odor concentrations.
As is evident from Fig. 7, however, there occurred an immediate adaptation in the olfactory bulbar response in salmon by infusing the home
water. It is impossible to assume that there exists such large odor
gradients as to overcome the adaptation. Hence, it is probable that the
orientation of these fish is not by osmotropotaxis but by “trial and error.”
Creutzberg (1958, 1959) reported that the elvers of eels, Anguilla
vulgaris, most probably used the tidal streams for their migration; they
are transported in the direction of the inland waters by the flood tide
and go to the bottom during the ebb in order not to be carried back to
sea. From the evidence obtained by preference experiments for the
waters, it is further suggested that elvers are guided from the open sea
to the inland water by olfactory cues and like adult salmon are thus
guided to their parent stream. Eels showed a clear preference for natural
freshwater originating from inland sources. The water lost its effectiveness
when passed through a charcoal filter. Recently, Miles (1968) reported
that elvers of the American eel Anguilla rostrata show a stronger positive
rheotaxis to freshwater than to saltwater. By the various treatment of the
water he also demonstrated that the attractive components dissolved are
biodegradable, heat stable, and nonvolatile; this seems to differ from the
substance that attracts salmon to their home stream (Fagerlund et al.,
1963; also see Volume VI, and Hara, 1970). Furthermore, the presence
of adult eels in the water made it more attractive, while the presence of
elvers made it less attractive. However, differences exist between the
salmon and the eel; knowledge of the cues seems to be acquired by
imprinting in the salmon, whereas it is most likely to be inborn in the
elvers. Recent studies of homing by tagging showed no clear evidence
that European eels (Anguilla anguilla) utilize olfactory cues to locate
their home area after transplantation over long distances up to a few
hundred kilometers off the coast (Tesch, 1967, 1970; Deelder and Tesch,
1970).
Bullheads, Zctalurus nebulosus and 1. natalis, have an extremely welldeveloped taste sense. Bardach et al. (1967a) have established that taste
alone can guide these fish to chemical clues. Bullheads seem to exhibit
true gradient searching in the absence of a current by spatial and temporal comparison of concentrations. Deprivation of the sense of smell
did not impair their searching ability, but unilateral deprivation of taste
receptors caused pronounced circling toward the intact side. Detailed
electrophysiological analysis of neural activity of the barbels in response
to chemical stimuli will greatly help to understand the mechanism under-
113
this fish is by spatial and temporal comparison of intensities, that speed
is related to the rate of change in stimulation, and that variation in turning serves to maintain fish at high odor concentrations.
As is evident from Fig. 7, however, there occurred an immediate adaptation in the olfactory bulbar response in salmon by infusing the home
water. It is impossible to assume that there exists such large odor
gradients as to overcome the adaptation. Hence, it is probable that the
orientation of these fish is not by osmotropotaxis but by “trial and error.”
Creutzberg (1958, 1959) reported that the elvers of eels, Anguilla
vulgaris, most probably used the tidal streams for their migration; they
are transported in the direction of the inland waters by the flood tide
and go to the bottom during the ebb in order not to be carried back to
sea. From the evidence obtained by preference experiments for the
waters, it is further suggested that elvers are guided from the open sea
to the inland water by olfactory cues and like adult salmon are thus
guided to their parent stream. Eels showed a clear preference for natural
freshwater originating from inland sources. The water lost its effectiveness
when passed through a charcoal filter. Recently, Miles (1968) reported
that elvers of the American eel Anguilla rostrata show a stronger positive
rheotaxis to freshwater than to saltwater. By the various treatment of the
water he also demonstrated that the attractive components dissolved are
biodegradable, heat stable, and nonvolatile; this seems to differ from the
substance that attracts salmon to their home stream (Fagerlund et al.,
1963; also see Volume VI, and Hara, 1970). Furthermore, the presence
of adult eels in the water made it more attractive, while the presence of
elvers made it less attractive. However, differences exist between the
salmon and the eel; knowledge of the cues seems to be acquired by
imprinting in the salmon, whereas it is most likely to be inborn in the
elvers. Recent studies of homing by tagging showed no clear evidence
that European eels (Anguilla anguilla) utilize olfactory cues to locate
their home area after transplantation over long distances up to a few
hundred kilometers off the coast (Tesch, 1967, 1970; Deelder and Tesch,
1970).
Bullheads, Zctalurus nebulosus and 1. natalis, have an extremely welldeveloped taste sense. Bardach et al. (1967a) have established that taste
alone can guide these fish to chemical clues. Bullheads seem to exhibit
true gradient searching in the absence of a current by spatial and temporal comparison of concentrations. Deprivation of the sense of smell
did not impair their searching ability, but unilateral deprivation of taste
receptors caused pronounced circling toward the intact side. Detailed
electrophysiological analysis of neural activity of the barbels in response
to chemical stimuli will greatly help to understand the mechanism under-