I have done no studies, and I know of no studies to confirm this, but I do have observations. Observations are the basis of Scientific investigation, so I offer the following.
In the Middle 80's I caught a rainbow trout in the Snake River, between Pocatello Idaho and Idaho Falls Idaho, that was about 16 inches long. This is not an area where many people would even consider C&R, so any trout caught is normally eaten. This fish had a gut on it that was massive. When I opened it up, it was full of rocks, about the size of marbles. The anus was over sized and distended, most likely from passing the rocks. The fish was healthy and strong.
In the early 90's, in a lake above Malad Idaho, I was ice fishing for Lake Trout. I opened up one of the nicer ones and found a rubber fluke style bait. Upon inspection, it was apparent the fish had tail grabbed the bait and ripped it from the hook. The fish was healthy and strong.
Around 2008, I caught a nice Triploid in Rufus Woods. When I opened it up, it had a 6" rubber curly tail worm in the stomach. It showed major deterioration of the worm, but the worm was in one piece. The fish was strong and healthy.
In the Post Falls Idaho Cabelas display aquarium, they had one trout that was eating rocks. It started doing this after they put crayfish in the tank. It was apparent that this fish loved to eat crayfish, and in the process it was "accidentally" picking up some rather large rocks. The fish had a rather grotesquely over sized stomach due to rocks of such a large size that they could not pass. The fish grew fast just like the other fish in the tank. Most of the other fish had a serious love of the crayfish as well, all had noses warn down from grubbing in the rocks, but only this one ate rocks. Eventually they had to remove the fish because of customer questions and complaints. The fish was healthy and strong the entire time I saw it.
In California some years ago a potential world record Large Mouth Bass was rejected when it was discovered that a 5 pound downrigger ball was in the gut. There was quite a stir over it at the time, and I remember that the angler was accused of putting the ball there. As I recall, the ball was coated with a cyst type material that the fish secreted to protect itself, so the ball must have been there for some time. The angler was vindicated, but the record was rejected. The fish obviously was doing just fine, at least up the the point of being caught and retained. LOL
Over the years I have caught fish of all species with rocks, sticks, plastic baits, moss, etc., in their stomachs. All were healthy enough to take my lure offering.
These observations have led me to a Hypothesis, the next step in the Scientific Method. I propose, or Hypothesize, that fish can retain indigestible items in the gut without adverse affects, sometimes to extremes.
The next step would require me to formulate an experiment to prove or disprove my hypothesis. Lacking the funds to do this, I would suggest that Burlee contact his friend and let the "fisheries school" perform the experiment. Until such an experiment disproves my hypothesis, I suggest that the preponderance of the evidence, the standard for non-criminal law, is sufficient to prove that non-digestible items in a fish's stomach are not harmful.
:study:
