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Weakfish sonic muscle: influence of size, temperature and season

M. A. Connaughton^1,*, M. L. Fine² and M. H. Taylor³

¹ Washington College, Department of Biology, 300 Washington Avenue, Chestertown, MD 21620, USA
² Department of Biology, Virginia Commonwealth University, Richmond, VA 23284-2012, USA
³ College of Marine Studies and Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA

View larger version (37K): [in a new window]   Fig. 1. (A) An illustration of the location of the sonic muscle in the weakfish Cynoscion regalis (modified from an illustration by H. L. Todd in Goode, 1884). (B) An oblique view of the swimbladder and associated sonic muscles; SM, sonic muscle; SB, lateral horn of the swimbladder; AP, aponeurosis overlying the dorsal surface of the swimbladder (modified from Ono and Poss, 1982). The swimbladder of a weakfish is approximately one-third of the total length of the fish, which ranged from 25 to 36 cm in our experiments. Figures taken from Connaughton et al. (1997).

View larger version (30K): [in a new window]   Fig. 2. Sonogram (A) and oscillogram (B) of a typical weakfish disturbance call consisting of a series of individual pulses of sound. Expanded oscillogram (C) of a single pulse consisting of 2-3 cycles of acoustic energy. Spectrum (D) of the pulse in C, demonstrating a dominant frequency of 480 Hz. Figures taken from Connaughton et al. (1997).

View larger version (16K): [in a new window]   Fig. 3. Relationship between dominant frequency and pulse duration for (A) fish ranging from 25 to 36 cm in total length (recorded at 18 °C, N=11) and (B) fish recorded at 12, 18 and 23 °C (28-31 cm in total length, N=8). (C) A plot of dominant frequency divided by a frequency calculated from the period of the second cycle of acoustic energy (shaded bar in inset). Frequency was calculated as [1000/(the duration of the second cycle of acoustic energy)]. Note that the dominant frequency is closely matched (expressed as values near to 1) by the inverse of the duration of the second cycle of acoustic energy. Figures modified from Connaughton et al. (2000).

View larger version (12K): [in a new window]   Fig. 4. Frequency and time-domain responses of low- and high-Q resonators. Acoustic data from a single weakfish pulse (A,B) express a wide bandwidth (arrows in A) and short duration (B, total duration less than 5 ms), typical of a low-Q, broadly tuned resonator. Acoustic data from a 440Hz tuning fork (C,D) express a narrow bandwidth (arrows in C) and a long duration (D, total duration more than 10s), common to a high-Q, tuned resonator (after Bradbury and Vehrenkamp, 1998). The time scales in C and D are the same as those in A and B.