Photographic identification of individual grayling, Thymallus thymallus, based on the disposition of black dots and scales



    1. Département de Biologie Animale et Ecologie. Université Lyon I. F-69622 Villeurbanne cedex, France (ERA CNRS No. 849 Ecologie des Eaux douces)
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SUMMARY. The flanks of grayling are generally studded with black dots which vary in number. The number and position of these dots are well-defined for each individual and make it possible to identify each fish, in some cases, as when there are very few dots or none at all, it is necessary to make use of other features such as the general disposition of the scales.

The best method for recording these characters is by photographing each fish. When recaptured, a fish can be recognized by comparing photographs. The number and position of dots on their lines can be sorted by a computer. Ultimate confirmation is given by comparing the most likely photographs once they have been selected by the computer.