Evaluation of Osmotic Induction of Calcein Treatments for Marking Juvenile Walleyes

Abstract

Osmotic induction of calcein was evaluated as a nonlethally detectable alternative to immersion in oxytetracycline for batch marking 42–58-d old walleyes Sander vitreus. A preliminary laboratory study and five larger-scale pond experiments were conducted to evaluate mark efficacy, mark retention, and tolerance to immersion in solutions of salt at 25 g/L or 50 g/L of water followed by immersion in a solution of calcein at 5 g/L of water. Walleyes became obviously stressed when immersed in the salt solutions, and mortalities immediately following the treatments ranged from 0% to 53%. All surviving walleyes possessed marks visible with a hand-held detector. However, the intensity of marks decreased exponentially on walleyes held in ponds, and only walleyes treated by initial immersion in the salt solution of 50 g/L possessed detectable marks when harvested 17–19 weeks posttreatment. The brightest marks occurred on structures most protected from sunlight. Marks on pelvic scales removed at time of capture also remained visible via epifluorescent microscopy for at least 2 weeks when stored in a freezer. These results suggest that osmotic induction of calcein would be a suitable method of producing nonlethally detectable marks for short-term stocking evaluations if techniques to reduce the stress induced by the marking process could be deployed.

Received December 12, 2011; accepted May 1, 2012

ACKNOWLEDGMENTS

We thank Jerre Mohler and Mary Negus for their technical advice on marking techniques and Seth Luchau for assistance in fish sampling and mark inspection. Mary Negus, David Staples, Steve Shroyer, Charles Anderson, and Donald Pereira also deserve thanks for providing constructive recommendations to an earlier draft of this manuscript.