Crayfish tracking of chemical stimuli in complex flow environments

Organisms from diverse taxa rely on chemical signals to gather diverse information about their environment. From salmon navigating vast oceans to return home to microbes initiating spore formation, chemical cues serve as vital sensory mechanisms. Yet, the strategies and behaviours used by animals to integrate hydromorphology and odourant properties remain to be elucidated. In our study, we investigated the responses of crayfish ( Pacifastacus leniusculus ) under three grades of flow complexities – low, medium, and high – created by stationary barriers under constant flow. Additionally, crayfish were exposed to two chemical cues: food and haemolymph. Over 30 minutes, the crayfish behaviour was recorded and analysed using Ethovision software. The results showed that crayfish in high flow complexity exhibited greater success in locating the cue's origin and increased exploration, enhancing their overall locomotory activity. The properties of the odourant significantly influenced navigation, with haemolymph triggering higher activity levels, greater distances moved, and increased velocities. Across all treatments, crayfish demonstrated increased presence in the cue area with high odour concentration and increased tracking along the edges of the arena. These findings underscore the complex relationship between hydrodynamic conditions and chemical signals in guiding animal behaviour.