Jim -

I've heard that question from folks that have fished with me. The answer is no, it doesn't seem to hurt the fish. I wouldn't use it on a small juvenile fish, but adult fish, certainly those 40" or bigger, arent' harmed in the least. Heck, on the big fish 50" and bigger, even the super spreader doesn't open their mouth that well. I would argue vigorously that this thing is acutually GOOD for the health of the fish by minimizing the time spent unhooking. Thanks, good question.