It is almost certain that birds, on very rare occasion move fish from one body of water to another. It is almost also certain that those believing they have witnessed this are sure of their observations. It is also well known that eye witness accounts are very often unreliable. We often see what we want to see. I have used the example of peanut allergy and early childhood exposure in my publications to illustrate why evidence-based medicine should always prevail over expert opinion. The peanut example actually shows how opinion, whether from an expert or not, should not overrule evidence, and I used this example to illustrate exactly that point. There have been more Elvis sightings than sightings of fish being stocked by birds, and in spite of cell-phone videos everywhere, no videos of birds moving fish have surfaced. This topic has been debated by ecologists for a very long time without resolution. I simply do not look to unlikely sources of fish stocking when there are billions of people on the planet. Having 3 different breeding fish populations show up in the same pond in a short period of time due to bird transport is like winning the lottery three times in a row - certainly possible, but very very unlikely.
https://www.scientificamerican.com/article/do-the-eyes-have-it/
