Acoustic activity of Litopenaeus vannamei fed pelleted and extruded diets

Passive acoustics monitoring (PAM) is an exceptional tool to analyze the feeding behavior of shrimp, as they emit a click sound by the mandibular occlusion. Hence, acoustic demand-feeding systems based on the click signals energy have been applied to improve feeding management in shrimp farming. These acoustic signals may be affected by the texture properties of the foods pellets, which are modified by the manufacturing process. The aim of the present study was to evaluate the acoustic activity of Litopenaeus vannamei fed pelleted and extruded diets. Two commercial diets were used, manufactured by extrusion and pelleting processing with similar formulation (36% crude protein) and pellet diameter. Acoustic evaluation was performed with these diets offered as is dry and previously soaked in water for one and two hours in a 2 x 3 factorial arrangement. The pellet hardness and moisture content were also measured. The acoustic trial was performed using omnidirectional hydrophones inside acoustic foam anechoic chambers. Three fastened shrimp (10 g) were placed inside acoustic chambers and audio recordings started (30 min) when food (0.5 g) was offered. The texture of diets was closely related to the acoustic intensity (Root Mean Square Amplitude - RMS) produced by L. vannamei during the feeding activity. The greater hardness of the extruded diet resulted in higher RMS than pelleted food when offered dry, which could be an advantage for the sound detection of feeding activity. The lower RMS observed when both diets were soaked suggests that softer texture pellets can be eventually ingested without the need of mandibles occlusion, and consequently without clicking sound emission. Additionally, unusual clicks train signals were first reported when shrimp fed soaked diets, probably due to mandibles rubbing. The relationship between textural properties and acoustical responses of foods should gain more attention, especially considering the potential applications on automatic acoustic feedback systems in shrimp farming.