I think it would be more precise to say that they are clipping "parr"...these fish are definitely too old and too big to be fry, or they would be way too small to clip.

Juvenile fish go through a physiological change that immediately precedes their transfer from fresh to salt water, interestingly enough called "smoltification". Many fish released from a hatchery may be as much as a year away from becoming "smolts".

So...now that we know that they aren't really releasing smolts, at least not all the time, and that they definitely weren't smolts at the time they were clipped, what does that do to answer the question?

Nothing, really...but they're definitely "parr" at the time of clipping.

Do parr have slime/scale damage during the clipping? Maybe, but the water they're put back into is generally pretty clean. I think they used to put them through a quick antibiotic wash right after clipping, but I don't know if they still do or not.

At that life stage they are also in full possession of their immune systems, which as was noted above, adults returning are not.

These little guys have three different stages of scale/slime...juvenile fresh water, saltwater, and adult fresh water. They are at their physiological touchiest at the transitions; they are not at a transitional stage at the time of clipping.

While there's no doubt that some handling damage must occur during clipping, my guess is that the extent of damage generally occurring is a lower amount of damage that has a lower impact at the time of clipping, versus handling at a transitional stage, where the damage would be both more extensive and of a higher impact.

Fish on...

Todd