Method for detecting a prone/supine position of fish conveyed by a conveying device. The method includes conveying the fish with the conveying device in a longitudinal direction, optically scanning a ventral side and a dorsal side of the fish in order to determine a first brightness value profile of a first side and a second brightness value profile of a second side, determining a first ordered data series and a second ordered data series by ordering brightness values of the first brightness value profile and of the second brightness value profile according to a predefined ordering criterion, determining a first median from the first ordered data series and a second median from the second ordered data series, determining at least one differential value from the first median and the second median, and determining the prone/supine position by comparing the at least one differential value with at least one predetermined reference value.