Michael L. Fine

Movement and sound generation by the toadfish swimbladder

Abstract. Although sound-producing (sonic) muscles attached to fish swimbladders are the fastest known vertebrate muscles, the functional requirement for such extreme speed has never been addressed. We measured movement of the swimbladder caused by sonic muscle stimulation in the oyster toadfish Opsanus tau and related it to major features of the sound waveform. The movement pattern is complex and produces sound inefficiently because the sides and bottom of the bladder move in opposite in and out directions, and both movement and sound decay rapidly. Sound amplitude is related to speed of swimbladder movement, and slow movements do not produce perceptible sound. Peak sound amplitude overlaps fundamental frequencies of the males mating call because of muscle mechanics and not the natural frequency of the bladder. These findings suggest that rapid muscle speed evolved to generate sound from an inefficient highly damped system.

Shallow-water propagation of the toadfish mating call

A mismatch between sound production and hearing in the oyster toadfish, Opsanus tau L., suggests the hypothesis that toadfish communicate over short distances. Low frequency acoustic signals (tones, noise and toadfish courtship calls) broadcast in 1 m deep water, attenuated rapidly, thereby restricting communication within a range of only several meters. Ambient noise does not appear to exert a strong selection pressure on the frequency spectrum of the boatwhistle or on the distance over which it is audible.

Variability in the role of the gasbladder in fish audition

Abstract The teleost gasbladder is believed to aid in fish audition by transferring pressure components of incoming sound to the inner ears. This idea is primarily based on both anatomical observations of the mechanical connection between the gasbladder and the ear, followed by physiological experiments by various researchers. The gasbladder movement has been modeled mathematically as a pulsating bubble. This study is extending the previous work on fish with a physical coupling of the gasbladder and ear by investigating hearing in two species (the blue gourami Trichogaster trichopterus, and the oyster toadfish Opsanus tau) without a mechanical linkage. An otophysan specialist (the goldfish Carassius auratus) with mechanical coupling, is used as the control. Audiograms were obtained with acoustically evoked potentials (e.g., auditory brainstem response) from intact fish and from the same individuals with their gasbladders deflated. In blue gourami and oyster toadfish, removal of gas did not significantly change thresholds, and evoked potentials had similar waveforms. In goldfish thresholds increased by 33–55 dB (frequency dependent) after deflation, and major changes in evoked potentials were observed. These results suggest that the gasbladder may not serve an auditory enhancement function in teleost fishes that lack mechanical coupling between the gasbladder and the inner ear.

SOMATIC AND OTOLITH GROWTH IN THE OYSTER TOADFISH (OPSANUS TAU L.)

Abstract Otoliths from oyster toadfish were measured and examined for annuli and daily increments. Distinct annual increments made it feasible to determine growth parameters which demonstrated sexual dimorphism in growth. Microincrements, judged to be daily on the basis of two separate criteria, were enumerated and measured to provide verification of annuli. Utilization of multivariate mathematical models relating age to otolith growth and somatic growth simplified age determination. These methods for examining otoliths should be applicable to other fish species and make it possible to link growth and mortality rates to life history and environmental occurrences.

Acoustic communication in two freshwater gobies: Ambient noise and short-range propagation in shallow streams

Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra were measured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200-500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations.

Pectoral Spine Locking and Sound Production in the Channel Catfish Ictalurus punctatus

We examined the anatomical basis for locking and sound production of the pectoral spine in the channel catfish, Ictalurus punctatus. We separate two related phenomena, binding and locking, both of which previously have been termed locking. Binding of the spine can occur in various partially abducted positions by applying muscular force to actively engage two friction-locking mechanisms. The spines dorsal process presses against the spinal groove of the cleithrum laterally, and its anterior process presses against a bony apron on the scapulocoracoid medially. Locking occurs when the spine is fully abducted and requires no additional muscular force. In this position, forward motion is prevented because the posterior end of the anterior process presses against an internal excavation in the lateral wall of the scapulocoracoid. Posterior motion is prevented by a catch that holds the anterior edge of the anterior process against the side of the elevated apron. The spine is unlocked by posterodorsally torquing the spine around its long axis, thereby lifting the edge of the anterior process above the imprisioning apron. Stridulation sounds are produced during spine abduction when ridges on the ventrolateral surface of the spines dorsal process contact the ventrolateral wall of the cleithrums spinal fossa. These sounds contain groups of pulses that vary in frequency, amplitude, duration, and pulse patterns. Individual pulses are generated by successive contacts of these ridges with the wall of the spinal fossa. The pulse frequency spectrum appears to be determined predominantly by the pectoral girdle, a nonspecialized acoustic radiator, and the swimbladder does not play an active role in sound production.

Acoustic pressure and particle motion thresholds in six sciaenid fishes.

SUMMARY Sciaenid fishes are important models of fish sound production, but investigations into their auditory abilities are limited to acoustic pressure measurements on five species. In this study, we used auditory brainstem response (ABR) to assess the pressure and particle acceleration thresholds of six sciaenid fishes commonly found in Chesapeake Bay, eastern USA: weakfish (Cynoscion regalis), spotted seatrout (Cynoscion nebulosus), Atlantic croaker (Micropogonias undulatus), red drum (Sciaenops ocellatus), spot (Leiostomus xanthurus) and northern kingfish (Menticirrhus saxatilis). Experimental subjects were presented with pure 10 ms tone bursts in 100 Hz steps from 100 Hz to 1.2 kHz using an airborne speaker. Sound stimuli, monitored with a hydrophone and geophone, contained both pressure and particle motion components. Sound pressure and particle acceleration thresholds varied significantly among species and between frequencies; audiograms were notably flatter for acceleration than pressure at low frequencies. Thresholds of species with diverticulae projecting anteriorly from their swim bladders (weakfish, spotted seatrout, and Atlantic croaker) were typically but not significantly lower than those of species lacking such projections (red drum, spot, northern kingfish). Sciaenids were most sensitive at low frequencies that overlap the peak frequencies of their vocalizations. Auditory thresholds of these species were used to estimate idealized propagation distances of sciaenid vocalizations in coastal and estuarine environments.

Lateralization of pectoral stridulation sound production in the channel catfish

Sounds of the channel catfish Ictalurus punctatus were found to consist of a rapid series of pulses produced by rubbing a ridged process on the first pectoral spine against the rough surface of a groove in the pectoral girdle during fin abduction. Although sounds can be made with either fin, approximately half of the individuals exhibited a fin preference, and 90% of these preferred the right fin. Unlike examples of handedness in other invertebrates and fishes, this preference is not simply a matter of anatomical asymmetry, but as in humans, reflects a preference between two equally developed limbs.

Crepuscular Changes in Emission Rate and Parameters of the Boatwhistle Advertisement Call of the Gulf Toadfish, Opsanus Beta

We quantified crepuscular variation in the emission rate and call properties of the boatwhistle advertisement call of Gulf toadfish, Opsanus beta, from a field recording of a natural population of nesting males in the Florida Keys. Their calls are more variable and complex than previously reported. A call typically starts with a grunt followed by one to five tonal boop notes (typically two or three) and lasts for over a second. The first boop is considerably longer than later ones, and intervals between boops are relatively constant until the final interval, which approximately doubles in duration. Positions of fish are fixed and calls are sufficiently variable that we could discern individual callers in field recordings. Calling rate increases after sunset when males tend to produce shorter calls with fewer notes. Analysis by number of notes per call indicates some individuals decrease the number of initial grunts and the duration of the first note, but most of the decrease results from fewer notes. To our knowledge this sort of call plasticity has not been demonstrated before in fishes. We suggest that call shortening lowers the chances of overlapping calls of other males and that the small amount of time actually spent producing sound (total on time) is an adaptation to prevent fatigue in sonic muscles adapted for speed but not endurance.

Comparison of sarcoplasmic reticulum capabilities in toadfish (Opsanus tau) sonic muscle and rat fast twitch muscle.

The sonic muscle of the oyster toadfish, Opsanus tau, can produce unfused contractions at 300Hz. Electron microscopy shows a great abundance of the Sarcoplasmic reticulum (SR) in this muscle, but no functional characterization of the capabilities of this SR has been reported. We measured the oxalate-supported Ca2+ uptake rate and capacities of homogenates of toadfish sonic muscle and rat extensor digitorum longus (EDL) muscle, and estimated the number of pump units by titration with thapsigargin, a high-affinity, specific inhibitor of the SR Ca-ATPase. The Ca2+ uptake rate averaged 70.9±9.5 mol min−1 per g tissue for the toad fish sonic muscle, and 73.5±3.7 mol min−1 g−1 for rat EDL. The capacity for Ca2+-oxalate uptake was 161±20 mol g−1 and 33±2 mol g−1 for toadfish sonic muscle and rat EDL, respectively. Thus, the rates of Ca2+ uptake were similar in the two muscles, but the toadfish sonic muscle had about five times the capacity of the rat EDL. The number of pumps as estimated by thapsigargin titration was 68±4 nmol of Ca-ATPase per g tissue in the toadfish, and 42±5 nmol Ca-ATPase per g tissue in the rat EDL. The turnover number, defined as the Ca2+ uptake divided by the number of pumps, was 1065±150 min−1 for toadfish and 1786±230 min−1 for rat EDL (p<0.05) at 37°C. The Ca2+ uptake rate of toadfish sonic muscle at 22°C, a typical temperature for calling toadfish, averaged 42±1% of its rate at 37°C. At these operating temperatures, the toadfish SR is likely to be slower than the rat fast-twitch SR, yet the toadfish sonic muscle supports more rapid contractions. One explanation for this is that the voluminous SR provides activator Ca2+ for contraction, but the abundant parvalbumin plays a major role in relaxation.