Comparison of Visible Implant Tags and Floy Anchor Tags on Hatchery Rainbow Trout

Abstract

Survival, effect on growth rate, tag readability and loss, and severity of injury were compared for 140–240-mm hatchery rainbow trout Oncorhynchus mykiss implanted with visible implant (VI) tags and Floy FD-68B fine-fabric anchor tags. Survival on six sampling dates over 120 d was always higher for fish tagged with VI tags than for fish tagged with Floy tags (e.g., 79 versus 68% at 120 d). Significantly more fish lost VI tags than Floy tags during the first 20 d of the experiment, but the difference was not significant by the end of the experiment (18 versus 11% offish remaining at 120 d). Most VI tags were lost either during the first 10 d or between 30 and 60 d, whereas Floy tags were lost gradually after 20 d. Overall, more rainbow trout with VI tags than with Floy tags were present at the end of the experiment (64 versus 59%), because the higher loss rate for VI tags was outweighed by the higher mortality of Floy-tagged fish. Rainbow trout with VI tags grew significantly faster than those with Floy tags, which produced a predicted difference of 9–10% in weight at 120 d for 50–100-g rainbow trout. At 120 d, 14% of VI tags were unreadable or readable only with light, whereas only 4% of Floy tags were as difficult to read. By the end of the experiment, 28% offish with Floy tags had moderate or severe injuries, whereas only 1% of those with VI tags were as severely injured. Our findings will aid biologists in choosing between VI and Floy anchor tags for specific applications.