Firstly, it's not a confirmed fact the the full Moon has an effect on the fishing in Fishao. There was a rumor about it during the full moon of July, but I was not really able to test it properly since I was unprepared with energy, bait etc.
So what I did was that I cast 200 times on nighttime between the 20th and the 21st, and 200 times during nighttime between the 21st and the 22nd.
Did I notice any difference? Well, actually yes. But it's hard to know if it was simply a coincidence and/or luck. But on the night between the 20th and 21st, among other things I caught three Pacuma Toadfish. And that fish doesn't bite very often. I have only caught it twice ever before. I also caught five Common Dolphinfish, quite a few Red Snappers as expected, and also some other common fish.
On the night between the 21st and 22nd my results where much poorer with fewer bites and simply nothing that special to report. I didnt have as many bites as on the previous night.
So that's pretty much it. Did I catch more fish during the full Moon? -Yes. Could it have been pure luck and coincidence? -Yes.