The loud crowd: Interactions between stocking density and acoustic feeding activity of different size classes of Litopenaeus vannamei

Passive acoustic monitoring (PAM) has been used to evaluate Litopenaeus vannamei feeding activity, as shrimp mandibles emit click sounds during food ingestion. PAM has also been used as a tool to estimate the population density of several aquatic species. Although stocking density is an important factor in shrimp farming, there is no information about its effect on shrimp acoustics during feeding activity. The present study aimed to explore the interactions between stocking density and acoustic activity of L. vannamei of different size classes under laboratory conditions. The trials were conducted in three circular fiberglass tanks using three shrimp stocking densities (50, 100 and 150 shrimp m-2) and four size classes (1, 3, 9 and 12 g). Recordings of feeding activity were carried out using omnidirectional hydrophones (sampling rate: 96 kHz; 16 bits) installed in each trial tank and lasted 30 min. Shrimp were fed with commercial pelleted diet and the uneaten food was collected to calculate the food consumption at the end of each recording. The clicks emitted by shrimp during acoustic recordings were automatically detect using Raven (R) acoustic software. The shrimp acoustic activity started immediately upon feed was offered, reaching the maximum click emission rate during the first minute and lasting up to about 10 min. The clicking emission rate shown a significant progressive increase from the lowest to the highest shrimp size class and stocking density, suggesting that a calibration approach can be applied to predict the population density when feeding sound signals are detectable. Significantly linear relationships between food consumption and number of clicks emitted by all size classes and stocking densities confirms that PAM is a feasible tool to estimate shrimp feed intake. Taken together, the present findings provide novel information about interactions between stocking density and acoustic activity that can contribute to research and development of feeding management in shrimp aquaculture.