152
WILLIAM N. TAVOLGA
properties. Swim bladder muscles in nonsonic fish may also possess this
reticulum and its associated fast-acting properties ( Kilarski, 1964). In
the catfishes, squirrelfishes, groupers, and sciaenids ( drumfish and
croakers), the sonic muscles are characteristically red in color as a result
of a high degree of vascularization, and this may enhance the resistance
to tetanization and fatigue. Histological examination of the sonic muscles
of these species showed uniformly thin fibers and numerous polyaxonal
innervations ( Gainer and Klancher, 1965).
The innervation of the sonic muscles shows features common to many
species. In the catfishes, the sonic muscle is supplied by a branch of the
occipital nerve (Tavolga, 1962). Except in certain Ostariophysi, there
are normally two pairs of occipital nerves in teleosts. Their homology
is uncertain, but they are presently thought to be homologous to the
hypoglossal ( XIIth) cranial nerve of the tetrapods. Based upon dissections, stimulation experiments, and serial cross sections, the nerve supply
to the sonic muscles was traced in the squirrelfish, toadfish, sea robin, and
red hind. Both pairs of occipital nerves were found to innervate these
muscles in all of the above species (Tavolga, 1964b). Except for the
sciaenids, in which sonic muscles are supplied by spinal nerves (Schneider
and Hasler, 1960), it appears that the innervation of the sonic muscles
in widely divergent teleosts is the same and that the muscles in all these
forms must be homologous structures, despite the gross differences in
appearance and location (Tavolga, 196413).
In the catfishes, if the swim bladder is damaged, deflated, or filled
with water, the sound output of the sonic muscle and the elastic spring
is greatly lowered, but the sound quality, i.e., its harmonic content, remains unchanged ( Tavolga, 1962). Winn and Marshall ( 1963) found
that in the squirrelfish, they could no longer detect the sound if the swim
bladder was completely filled with water. Partial deflation of the bladder
reduced the sound amplitude but did not affect the fundamental frequency or other properties (also true for other species: Salmon et al.,
1968). In toadfishes, if the swim bladder was partially deflated, the spontaneous grunting sounds continued to have the same spectral characteristics but showed a reduced amplitude by as much as 20 dB (Tavolga,
196413). It does not appear likely, therefore, that the resonating role of
the swirn bladder is an important one, especially since the excess internal
pressure in the swim bladders of most fishes is low (Alexander, 1959a,b).
The pulsation of the bladder should be essentially that of a large air
bubble and would be affected by the low compressibility of the medium
and a variety of other physical factors. The net result is a damping of
the resonance and a decrease in the resonant frequency. Based on the
formula given by Meyer (1957), the resonant frequency of a bubble of air
WILLIAM N. TAVOLGA
properties. Swim bladder muscles in nonsonic fish may also possess this
reticulum and its associated fast-acting properties ( Kilarski, 1964). In
the catfishes, squirrelfishes, groupers, and sciaenids ( drumfish and
croakers), the sonic muscles are characteristically red in color as a result
of a high degree of vascularization, and this may enhance the resistance
to tetanization and fatigue. Histological examination of the sonic muscles
of these species showed uniformly thin fibers and numerous polyaxonal
innervations ( Gainer and Klancher, 1965).
The innervation of the sonic muscles shows features common to many
species. In the catfishes, the sonic muscle is supplied by a branch of the
occipital nerve (Tavolga, 1962). Except in certain Ostariophysi, there
are normally two pairs of occipital nerves in teleosts. Their homology
is uncertain, but they are presently thought to be homologous to the
hypoglossal ( XIIth) cranial nerve of the tetrapods. Based upon dissections, stimulation experiments, and serial cross sections, the nerve supply
to the sonic muscles was traced in the squirrelfish, toadfish, sea robin, and
red hind. Both pairs of occipital nerves were found to innervate these
muscles in all of the above species (Tavolga, 1964b). Except for the
sciaenids, in which sonic muscles are supplied by spinal nerves (Schneider
and Hasler, 1960), it appears that the innervation of the sonic muscles
in widely divergent teleosts is the same and that the muscles in all these
forms must be homologous structures, despite the gross differences in
appearance and location (Tavolga, 196413).
In the catfishes, if the swim bladder is damaged, deflated, or filled
with water, the sound output of the sonic muscle and the elastic spring
is greatly lowered, but the sound quality, i.e., its harmonic content, remains unchanged ( Tavolga, 1962). Winn and Marshall ( 1963) found
that in the squirrelfish, they could no longer detect the sound if the swim
bladder was completely filled with water. Partial deflation of the bladder
reduced the sound amplitude but did not affect the fundamental frequency or other properties (also true for other species: Salmon et al.,
1968). In toadfishes, if the swim bladder was partially deflated, the spontaneous grunting sounds continued to have the same spectral characteristics but showed a reduced amplitude by as much as 20 dB (Tavolga,
196413). It does not appear likely, therefore, that the resonating role of
the swirn bladder is an important one, especially since the excess internal
pressure in the swim bladders of most fishes is low (Alexander, 1959a,b).
The pulsation of the bladder should be essentially that of a large air
bubble and would be affected by the low compressibility of the medium
and a variety of other physical factors. The net result is a damping of
the resonance and a decrease in the resonant frequency. Based on the
formula given by Meyer (1957), the resonant frequency of a bubble of air