Do I even want to ask what you left in the livewell? I bet it is RIPE!!!
Wife said to sell the boat.
All kidding aside. I would try one of those citrus cleaners, non-toxic and flush with lots of fresh water. Whatever you use make sure it does not leave any residue in the tank to kill future live bait.
Spray Nine is a good cleaner and can be obtained at Boaters World but be sure to rinse it well. When you are done, if you can still smell it then it's not rinsed enough!