Preliminary Results of Tetracycline Labelling for Validating Annual Growth Increments in Opercula of Walleyes

Tetracycline was injected into 144 walleyes (Stizostedion vitreum vitreum) from Wapun Lake, Manitoba, in 1978 to validate the use of the operculum for age determination. Fish were tagged and injected at a rate of either 50 or 100 mg tetracycline/kg body weight; they were held for 1 h in a recovery tank, then released back into the lake. Over the succeeding 2 years, 10 injected fish were recaptured. Tetracycline was deposited in the opercula of all recaptured, injected fish as a yellow-green fluorescent band that was visible under ultraviolet light. Complete agreement was achieved between the number of observed annual growth increments laid down on the opercula since injection and the number of years the fish were at large.