<p>Avoidance reaction rates of fish in daylight (top) and dark (bottom) conditions referred to 25 cm wide flume volume segments (N = 38) set virtually along the x-axis of the experimental flume (grey) and fitted GAM function (solid line).</p>

<p>The different hydraulic zones along the flume x axis are marked by the colored bar above each graphic, in daylight where the trout specific threshold for SVG of 0.31 m/s/m is available from our experiments the for zones (Approach zone:- < 0.31 ; <; zone: > 0.31 ; <; Mixed zone: > 0.31 ; ≥ ; High velocity zone: < 0.31 ; ≥ ) are distinguished, whereas for the dark conditions along the flume x axis only a distinction between low velocity zone ≤ and low velocity zone ≥ was possible; the end of the SVG zone (daylight) or low velocity zone (dark) and the start of the mixed zone (daylight) or high velocity zone (dark) depend on the body length-dependent maximum sprint speed of each fish, this causes a fuzzy boundary between SVG/mixed zone or low/high velocity zone.</p>