Flow impairs multisensory tracking and increases active sensing in weakly electric fish

Weakly electric fish rely on electrosensory, visual and mechanosensory (lateral-line) cues to guide behavior in flowing water, yet the effects of ambient currents on multisensory tracking and active sensing remain poorly understood. We tested the weakly electric knifefish Apteronotus albifrons (n=4) tracking a moving refuge in a recirculating flow tunnel while systematically varying flow speed (0-16 cm s-1), illumination (light versus dark) and refuge structure (windowed versus non-windowed). Tracking performance was quantified with time- and frequency-domain measures (root-mean-square error; gain-phase analyses), and active sensing as movement power outside stimulus frequencies (mean active sensing power, MASP). Increasing flow degraded tracking: relative to still water, RMSE rose by ∼46% at 16 cm s-1. Deficits were largest in darkness and with the windowed refuge, and were concentrated at low stimulus frequencies. Under higher flows, fish showed a trend toward increased off-frequency movement power (by ∼33%), consistent with compensatory active sensing to sustain sensory acquisition. The effects were non-linear and context dependent. This pattern indicates that increasing hydrodynamic noise may drive dynamic reweighting among visual, electrosensory and mechanosensory inputs. Collectively, our data indicate that ambient flow degrades low-frequency tracking and may elicit compensatory active sensing in A. albifrons, extending recent demonstrations of context-dependent sensing and control switches in this species and bridging rheotaxis with electrosensory refuge tracking.