[porgylber]

First off, you were scammed, sorry to say. My best guess is a foreign object (like a sinker) was shoved down the throat of the “winning” fish.
Unfortunately, I can kind of relate. About 7 or 8 years ago, I was on a party boat out of Central NJ. The boat was packed, easily more than 50 anglers on board. I was fortunate enough to catch the largest, pool winner. When it came time to collect, the mate handed me a 20 dollar bill.
I knew this was wrong, so I asked where the rest was. She ( it was a female) told me the total pool was $20!!!
This was total BS...and to this day, I have never set foot on that boat again. In retrospect, I should have raised a stink with the Captain. However, due to their dishonesty, they have cost themselves easily a couple of thousand dollars over the subsequent years in lost fares from me.

I have been fortunate to win a few pools over the following years on other boats. I have always been troubled by the fact that the system is so unregulated. The overwhelming majority of boats are honest...but as you saw, and I have seen, shenanigans do take place. Perhaps collecting the money and placing it in a clear container that all can see would eliminate my issue.

As for your issue, all that can be done is to fully examine the fish if you suspect cheating.