Acoustic characterization of feeding activity of Litopenaeus vannamei in captivity

The aim of the present study was to evaluate the acoustic activity of Litopenaeus vannamei of different size classes during feeding in captivity, as well as describe the sound generation mechanism and main associated acoustic variables. The structure responsible for sound emission was identified based on simultaneous audio and video recordings during the consumption of feed pellets. Eighteen animals divided into three size classes (small: 13.03 ± 1.87 g; medium: 22.09 ± 2.20; large: 35.31 ± 3.20 g) were used for the acoustic characterization of feeding activity. The animals were fed three pellets (48 ± 4 mg) individually and offered in sequence. The recording of each pellet offered lasted 10 min, beginning with the point at which the animal took the pellet. The number of sound pulses (“clicking” sound) per pellet ingested was counted and related to food intake. L. vannamei emits sound during the feeding process, which is associated with the closing of the mandibles during the shredding of the food. The average values for the acoustic variables were a minimum frequency of 3.47 ± 0.32 kHz, maximum frequency of 37.75 ± 2.44 kHz, frequency peak of 11.1 ± 3.39 kHz, maximum energy of 83.55 ± 3.39 dB and sound duration of 4.7 ± 0.2 ms. No statistically significant differences in the acoustic variables were found among the different size classes or in the sequence of the pellets offered. The number of clicks per pellet ranged from 121 to 154 for all size classes. However, the number of clicks generated in the large class was significantly higher during the first minute after the capture of the pellets, dropping significantly after five minutes in comparison to the other size classes. The findings demonstrate that L. vannamei is acoustically active and the sounds generated can be used as an indication of feeding activity in captivity. The click rate per pellet or particular period of time, combined with the maximum energy generated at a specific frequency (frequency peak) can be used as an indication of the quantity of feed consumed by the animals.