A pixel luminosity method was tested to assess mark quality in fish otoliths using allis shad Alosa alosa L. larvae. Five-day old larvae were marked at different concentrations (200-250-300ppm) of tetracycline hydrochloride and for different durations (4-6h). Mark quality was assessed for 15 and 32-day old fish. The pixel luminosity method provided a better discrimination of mark quality between the different treatments compared to the visual estimation. Also, it is strongly recommended to take into account the otolith background fluorescence while reporting mark intensity, to reveal the true success of the marker incorporation. The pixel luminosity method offers a good alternative for handling the subjectivity of visual estimation.