Characterization of detection and attractivity behaviour of the Pacific white shrimp Litopenaeus vannamei

Introduction: Litopenaeus vannamei is an omnivorous shrimp species with a scavenger tendency. Its clear preference for feed containing high proportion of marine animal products lead to unsustainable feed formulas. Continues and impressive efforts have been made by feed formulators to spare marine proteins with alternative raw materials. One of the actual limits of this process is the poor attractivity and palatability of those ingredients for the shrimp. There is a consequent need to characterize feed ingredients based on their capacity to attract the shrimp toward sustainable pellets. Ethograms such as the one established by Lee and Meyers (1996) could be improved thanks to new observation methods. The goal of this study was to observe and analyze individual behaviors of shrimp confronted with pellets or dissolved amino acids (AA). This work was divided into two experiments: the first (Exp I) looked at the behavior of shrimp when confronted with feed pellets and the second one (Exp II) looked at their behavior when confronted with free AA dissolved in water.Materiel and Methods Twenty PL20 L. vannamei were bought in a commercial shrimp farm and acclimatized in Halieutica research station (Angers, France).In Exp I, 14 shrimp were tested individually in a random order. Each animal was successively placed in a close tank filled with artificial marine water (salinity 30ppt, temperature 27°C) and was acclimatized for 5 minutes. At this time, experimental pellets were introduced in the tank. Animal behavior was recorded from above for ten minutes. Videos were analyzed in order to find characteristic behaviors of detection and attractivity. In Exp II 6 individuals were tested individually in a random order. Animal were placed in a small recycling aquaculture system made of two tanks. Animal were kept in a first tank, which was the same tank as in Exp I. The second tank was used as a buffer tank. After 5 minutes of acclimatization, different quantities of a dissolved mix of free amino acids (MFAA, KERASTIM® 50, BCF Life Sciences, France) were placed in the second tank (0ppm; 30ppm; 60ppm and 90ppm). Water movements between the two tanks were allowed by a peristaltic pump (Fig. 1). Animal behavior was recorded for 5 minutes before the adding of amino acids and 5 minutes after. Video recording and analysis were performed the same way as during Exp I. For the observed behaviors, statistical analysis have been performed in order to show a potential effect of the concentration of MFAA, and an effect of the adding of pellets. Permutation test and Wilcoxon post hoc were made using RStudio (version 4.2.1). Results For both experiments, the main behaviors observed were immobility duration, antennal, antennular and scaphocerites flicking and eye beats. In Exp. I none of those behaviors were significantly impacted by pellet addition. A tendency was however observed for antennal and antennular flicking, eye beat and immobility duration. In Exp. II, behaviors significantly influenced by the concentration of MFAA dissolved in water were immobility duration and scaphocerites flicking. A tendency was shown on antennal and antennular flicking.Animal behaviors analysis resulted in a classification of the individuals within three different groups for each stimulus.Discussion/ConclusionResults obtained through this preliminary study did not allow us to create a clear ethogram. There was a strong individual variability in the studied behaviors. It could be the sign that every shrimp behave differently. Thus, it could be interesting to further this study with a higher number of individuals or to test individuals in groups