6. SOUND PRODUCTION AND DETECTION
151
insert on the first pairs of ribs. These muscles contract against the tension
of hypaxial muscles, vertebral ligaments, and connective tissue lacings
to the roof of the swim bladder (Hazlett and Winn, 1962; Winn and
Marshall, 1963). In the sea robins and toadfishes, where the sonic muscles
are intrinsic to the swim bladder, the elasticity of the bladder walls and
the internal pressure of the distended bladder will tend to return the
muscle fibers to normal length after each contraction. In the sciaenids, the
return of the sonic muscles to normal shape after contraction is a function
of the swim bladder tension, in part, and probably a function of the elasticity of the lateral body wall musculature. In catfishes, Tavolga (1962)
showed that the fundamental frequency of the sound is a direct translation of the frequency of contraction of the muscle. Packard (1960) recorded sounds and muscle action potentials simultaneously in the pigfish, Congiopodus, from New Zealand, and he found that the contraction
frequency coincided with the sound frequency. A similar observation was
made by Barber and Mowbray (1956) in the sculpin and Schneider
(1964b, 1967) in Therapon. Winn and Marshall (1963) found that each
sound from a squirrelfish, Holocentrus rufus, consisted of up to 5 pulses,
about 10 msec apart. This corresponds to a fundamental frequency of
about 100 Hz. Muscle action potentials coincided with the pulses.
Artificial stimulations of nerves leading to the sonic muscles can show
that the muscles are capable of unusually rapid contraction and recovery
cycles. In the gaff-topsail catfish, Bagre marinus, the sonic muscles took
up to 12 sec to tetanize at 150 pulses/sec, and up to 3 sec at 200 pulses/
sec ( Tavolga, 1962). Using the same stimulating equipment as described
earlier (Tavolga, 1962), the nerves leading to the sonic muscles were
stimulated in the toadfish, Opsanus tau, the slender sea robin, Prwnotus
scitulus, the squirrelfish, Holocentrus ascensionis, and the red hind,
Epinephelus guttatus. Opsanus and Priorwtus muscles were found to be
most resistant to tetanization, but all could be stimulated at pulse frequencies over 100/sec without tetanization ( Tavolga, 1964b).
Among vertebrates, the occurrence of such fast-acting muscles is
unusual. Extrinsic eyeball muscles are known to reach 350 contractions/
sec, but the majority become tetanized when stimulated at 50 pulseslsec.
The sonic muscle of Opsanus has a contraction-relaxation cycle of 10 msec
( Skoglund, 1959), which would theoretically limit its response to about
100 contractions/ sec, but Skoglund's observations were limited to single
twitches. Sonic muscles in the squirrelfish show fusion at frequencies
above 200/sec, while normal white muscle begins to show summation at
50 and fusion at 100 pulses/sec (Gainer et al., 1965). Electron microscopy
showed the presence of an unusually developed sarcoplasmic reticulum
which Fawcett and Revel (1961) have related to the muscle's fast-acting
151
insert on the first pairs of ribs. These muscles contract against the tension
of hypaxial muscles, vertebral ligaments, and connective tissue lacings
to the roof of the swim bladder (Hazlett and Winn, 1962; Winn and
Marshall, 1963). In the sea robins and toadfishes, where the sonic muscles
are intrinsic to the swim bladder, the elasticity of the bladder walls and
the internal pressure of the distended bladder will tend to return the
muscle fibers to normal length after each contraction. In the sciaenids, the
return of the sonic muscles to normal shape after contraction is a function
of the swim bladder tension, in part, and probably a function of the elasticity of the lateral body wall musculature. In catfishes, Tavolga (1962)
showed that the fundamental frequency of the sound is a direct translation of the frequency of contraction of the muscle. Packard (1960) recorded sounds and muscle action potentials simultaneously in the pigfish, Congiopodus, from New Zealand, and he found that the contraction
frequency coincided with the sound frequency. A similar observation was
made by Barber and Mowbray (1956) in the sculpin and Schneider
(1964b, 1967) in Therapon. Winn and Marshall (1963) found that each
sound from a squirrelfish, Holocentrus rufus, consisted of up to 5 pulses,
about 10 msec apart. This corresponds to a fundamental frequency of
about 100 Hz. Muscle action potentials coincided with the pulses.
Artificial stimulations of nerves leading to the sonic muscles can show
that the muscles are capable of unusually rapid contraction and recovery
cycles. In the gaff-topsail catfish, Bagre marinus, the sonic muscles took
up to 12 sec to tetanize at 150 pulses/sec, and up to 3 sec at 200 pulses/
sec ( Tavolga, 1962). Using the same stimulating equipment as described
earlier (Tavolga, 1962), the nerves leading to the sonic muscles were
stimulated in the toadfish, Opsanus tau, the slender sea robin, Prwnotus
scitulus, the squirrelfish, Holocentrus ascensionis, and the red hind,
Epinephelus guttatus. Opsanus and Priorwtus muscles were found to be
most resistant to tetanization, but all could be stimulated at pulse frequencies over 100/sec without tetanization ( Tavolga, 1964b).
Among vertebrates, the occurrence of such fast-acting muscles is
unusual. Extrinsic eyeball muscles are known to reach 350 contractions/
sec, but the majority become tetanized when stimulated at 50 pulseslsec.
The sonic muscle of Opsanus has a contraction-relaxation cycle of 10 msec
( Skoglund, 1959), which would theoretically limit its response to about
100 contractions/ sec, but Skoglund's observations were limited to single
twitches. Sonic muscles in the squirrelfish show fusion at frequencies
above 200/sec, while normal white muscle begins to show summation at
50 and fusion at 100 pulses/sec (Gainer et al., 1965). Electron microscopy
showed the presence of an unusually developed sarcoplasmic reticulum
which Fawcett and Revel (1961) have related to the muscle's fast-acting