Where is my giant monster fish?

So I was doing the fishing festival trying to somehow win against the cheating ai (looking at you gunther) and as I fish I catch some humongous fish that looked more like a dolphin, a sturgeon sized in 549 cm, holy heck! thats big. So obviously I win the festival in the biggest fish category and as i go to check my bag, I dont see the fish. Where did it go? Was It a miracle of RNG or you dont keep big ones?