Norm--About 3 or 4 years ago we tagged bass in our 2 acre pond with the T-anchor style tags and we still catch some fish with tags in them. I'm sure there is not 100% retention but there are still plenty with tags in them.Some have infected looking spots where the tag was inserted although their overall health seems fine.
I worked for a fisheries research station and one of the projects was how well certain types of clips and marks would show up over the years. Some were freeze branded and others received various clips. Results were extremely varied. Some fish had well defined clips 3 years later, some grew back but you could tell IF you looked very closely, and others showed no signs of being clipped. Those bass ranged from 12-18 inches. We would also have tagged bass in lakes that tagged when they were 6-8 inches and we recovered them at 16-18 inches still clipped. If you don't want to tag them I would clip the pelvic fins as close to the body as possible with scissors and if possible trim the fins up when they get recaptured later on. What kind of project are you working on? We tagged ours to look at individual growth. I'd highly recommend buying the numbered tags for doing this. I tried the cheaper route by numbering my own tags, but after a year or so algae covered the tag making it virtually impossible to rub off without rubbing off the numbers. I can still read one from time to time, but not most. Good luck.
Mike
