The Advantage to Fishes of Hovering in Shade

target. This relative visual advantage may result from two interacting visual phenomena: 1) the increment threshold response, whereby a sunlit viewer has a raised contrast perception threshold and therefore has difficulty responding to a shaded target; and 2) the veiling brightness effect, whereby particles between sunlit observer and shaded target scatter relatively bright light into the observer's eyes, further reducing the target's visual contrast. Shade-producing objects may attract fishes because the objects function to reduce both background light and veiling brightness. A fish hovering in shade is better able to see approaching objects and is simultaneously more difficult to see.