White-leg shrimp (Litopenaeus vannamei) as an important aquatic economic species in the world, behavioral acoustics research will help to improve the level of aquaculture. In the present study, two sizes of the white-leg shrimp (4—6 cm TL and 10—11 cm TL) from the nursery of Shanghai Ocean University were investigated. The experiment was conducted in 2 glass tanks (4 cm×28 cm×30 cm) which were shaded. In addition, there were two controllable underwater lights of 10W in each tank. One underwater camera and one hydrophone were fixed in each tank. The hydrophone was 20 cm away from the top and connected to an SM4 recorder. Prior to the experiment, the controlled underwater light and the underwater camera (turned on before placing the water) are placed in the desired location. For each measurement, individual white-leg shrimp was used and acclimated for 40—60min under the dark prior to measuring. Sounds were recorded for 10 minutes after the lights were switched on (a timer controlled the time). Meanwhile, the behaviors of the white-leg shrimp were captured by the underwater camera.
The results showed that the main peak frequency of the acoustic signals was about 250 Hz, and the secondary peak appeared near 425 Hz produced by the small white-leg shrimp during fast swimming. The primary peak frequency of acoustic signals was 70 Hz, and the secondary peak was 15 Hz produced by the large shrimp. Further, the center frequency and frequency range of the acoustic signals of the tail flick was significantly different from that of the fasting swimming. We also collected a signal of tail flick from the white leg shrimp in the shrimp pond. The energy range of the signal was 0.5—6 kHz. The energy frequency range was 1—4 kHz, and the maximum concentrated energy frequency was about 2 kHz. Different from the laboratory’s results, the main peak frequency of the signal was about 1.8 kHz, and there was a main secondary peak of about 250 Hz. In comparison to the laboratory data, the pond background noise and the sound produced by the white-leg shrimp during fast swimming were low-frequency signals. The frequency of the signal by tail-flick of the white-leg shrimp was higher than the background noise. The signal duration in the pond and laboratory was about 0.01s, and the frequency distribution of the energy was concentrated at 2—3 kHz. In summary, we studied the fast swimming sound production by two size white-leg shrimp. In the future, the tail flick sounds produced by shrimps of different conditions need further study, which is essential to utilizing sound information for monitoring shrimp health.
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