Connaughton M A, Fine M L, Taylor M H
Washington College, Department of Biology, 300 Washington Avenue, Chestertown, MD 21620, USA.
J Exp Biol. 2002 Aug;205(Pt 15):2183-8. doi: 10.1242/jeb.205.15.2183.
The influence of temperature, size and season on the sounds produced by the sonic muscles of the weakfish Cynoscion regalis are categorized and used to formulate a hypothesis about the mechanism of sound generation by the sonic muscle and swimbladder. Sounds produced by male weakfish occur at the time and location of spawning and have been observed in courtship in captivity. Each call includes a series of 6-10 sound pulses, and each pulse expresses a damped, 2-3 cycle acoustic waveform generated by single simultaneous twitches of the bilateral sonic muscles. The sonic muscles triple in mass during the spawning season, and this hypertrophy is initiated by rising testosterone levels that trigger increases in myofibrillar and sarcoplasmic cross-sectional area of sonic muscle fibers. In response to increasing temperature, sound pressure level (SPL), dominant frequency and repetition rate increase, and pulse duration decreases. Likewise, SPL and pulse duration increase and dominant frequency decreases with fish size. Changes in acoustic parameters with fish size suggest the possibility that drumming sounds act as an 'honest' signal of male fitness during courtship. These parameters also correlate with seasonally increasing sonic muscle mass. We hypothesize that sonic muscle twitch duration rather than the resonant frequency of the swimbladder determines dominant frequency. The brief (3.5 ms), rapidly decaying acoustic pulses reflect a low-Q, broadly tuned resonator, suggesting that dominant frequency is determined by the forced response of the swimbladder to sonic muscle contractions. The changing dominant frequency with temperature in fish of the same size further suggests that frequency is not determined by the natural frequency of the bladder because temperature is unlikely to affect resonance. Finally, dominant frequency correlates with pulse duration (reflecting muscle twitch duration), and the inverse of the period of the second cycle of acoustic energy approximates the recorded frequency. This paper demonstrates for the first time that the dominant frequency of a fish sound produced by a single muscle twitch is apparently determined by the velocity of the muscle twitch rather than the natural frequency of the swimbladder.
温度、体型和季节对犬牙石首鱼（Cynoscion regalis）发声肌肉所产生声音的影响被分类整理，并用于构建一个关于发声肌肉和鱼鳔发声机制的假设。雄性犬牙石首鱼发出的声音出现在产卵的时间和地点，并且在圈养环境中的求偶行为中也被观察到。每次鸣叫包含一系列6 - 10个声脉冲，每个脉冲呈现出由双侧发声肌肉同时单次抽搐产生的衰减的2 - 3个周期的声学波形。在产卵季节，发声肌肉的质量增加两倍，这种肥大是由睾酮水平升高引发的，睾酮水平升高会促使发声肌肉纤维的肌原纤维和肌浆横截面积增加。随着温度升高，声压级（SPL）、主频和重复率增加，脉冲持续时间减少。同样，随着鱼体型增大，声压级和脉冲持续时间增加，主频降低。声学参数随鱼体型的变化表明，在求偶过程中，击鼓般的声音有可能作为雄性健康状况的“诚实”信号。这些参数也与发声肌肉质量的季节性增加相关。我们假设发声肌肉的抽搐持续时间而非鱼鳔的共振频率决定主频。短暂的（3.5毫秒）、迅速衰减的声脉冲反映出一个低Q值、宽调谐的谐振器，这表明主频是由鱼鳔对发声肌肉收缩的受迫响应所决定的。相同体型的鱼随着温度变化而改变的主频进一步表明，频率并非由鱼鳔的固有频率决定，因为温度不太可能影响共振。最后，主频与脉冲持续时间相关（反映肌肉抽搐持续时间），并且声能第二个周期的周期倒数近似于记录的频率。本文首次证明，由单次肌肉抽搐产生的鱼类声音的主频显然是由肌肉抽搐的速度而非鱼鳔的固有频率决定的。
