The use of bird rings for the individual recognition of fish

Abstract

SUMMARY. Fish bearing celluloid bird rings on the anterior edge of the dorsal fin can be recognized individually in the field for several weeks. Grayling Thymallus thymallus, over 20 cm long, in a fast‐flowing river retained recognisable rings for a mean of 47 days. Brown trout Salmo trutta, retained rings for comparable periods. Rings could be seen at distances up to 10 m, irrespective of the orientation of the fish to the observer. This marking technique compares favourably with others.