Carnival fish are in the plastic bags, so can i have one in a regular beta tank?

Sigh, I wish carnivals would stop using goldfish as prizes and having ping pong balls thrown at them. By betta tank, assume it's 5 gallons or even less? Then pretty inappropriate for a goldfish. Better than a bowl, but still pretty poor. Goldfish produce large amounts of waste and can quickly pollute their tanks, and the carnival ones grow the largest, up to over a foot in length. They need a heavy duty filter and no heater, and bubblers aren't necessary. Sadly, common/comet goldfish do best in large tanks around 50 gallons, because of their size and waste output. They were bred for pond life.