在电影《大白鲨》中，当这条凶恶的鲨鱼在水中游弋时，约翰-威廉姆斯那带有不祥预感的音乐便会响起。
然而水虎鱼却有着它们自己的伴奏。红腹水虎鱼（Pygocentrus nattereri）在进行捕猎时会发出恼人的噪音。为了搞清这种小鱼是如何在水下发声的，比利时列日大学生物学家Sandie Millot在一个鱼缸中对它们进行了观察。研究人员发现，这种凶猛的猎食者会发出3种声音：首先，当一条水虎鱼同对手面对面时，它们会发出急促的叫声，就如同犬吠一般。而在两条鱼搏斗的整个过程中，水虎鱼往往会发出两声低沉的吼叫。斗志旺盛的水虎鱼利用肌肉快速击打自己的鱼鳔——帮助它们漂浮的气室——来发出这两种声音。而第三种叫声则最令人厌恶——水虎鱼会不停地撞击它们的牙齿以驱赶其他的鱼远离自己的晚餐。研究人员在本月出版的《实验生物学期刊》上报告了这一研究成果。(生物谷 Bioon.com)
doi:10.1242/?jeb.061218
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PMID:
Sound production in red-bellied piranhas (Pygocentrus nattereri, Kner): an acoustical, behavioural and morphofunctional study
Sandie Millot, Pierre Vandewalle and Eric Parmentier
Piranhas are known to be sound-producing animals. Nevertheless, the biological significance of piranha calls remains unclear because sounds have been recorded only when specimens were held by hand or trapped in a gill net. These sounds are generated by rapid contractions of sonic muscles that insert on a broad tendon surrounding ventrally the cranial sac of the swimbladder. The piranha swimbladder is thought to play an important role in sound production as an impedance-matching device and as a resonator. However, the vibratory capacities of the cranial and caudal sacs and the exact role of both sacs in sound production remain poorly understood. In this study, three sounds were each associated to a specific behaviour. The first sound (type 1) was produced during frontal display; it had numerous pulses and lasted 140!±17 ms, with a fundamental frequency of 120±4 Hz. It corresponded to the sound made by hand-held fishes. The second sound (type 2) was produced during circling and fighting behaviour; it was a single pulse lasting 36±8 ms, with a fundamental frequency of 43±10 Hz. The third sound (type 3) corresponded to chasing behaviour and comprised three to four pulses, each lasting 3±1 ms, with a fundamental frequency of 1739±18 Hz. Using a laser vibrometer to study the swimbladder displacement when stimulated at different frequencies, it was demonstrated that the first two sounds corresponded to the swimbladder mechanism. By contrast, the third sound was associated with the jaw mechanism. The vibrometer indicated that the swimbladder is a highly damping structure, simply copying the sonic muscle contraction rate. This study provides two interesting insights. First, it shows the relationships between three kinds of piranha sound and three specific behaviours. Second, using muscle stimulation at different rates, it shows which simultaneous conditions are required for production of sound in this species. Swimbladder calls were produced by a muscle contraction rate of approximately 100 Hz because this periodicity allowed the swimbladder to vibrate. At this frequency range, the contraction–relaxation cycles of the swimbladder muscles engendered wall displacements that had short amplitudes and with only a small variability between them.
