Goldfish can reach 20" and 6+ pounds. There are feral populations in the Potomac River that are likely over 100 years old. When running a seine in the river, I regularly catch the natural olive drab reverted colored young. In the spring, it's not uncommon to see numerous mostly drab colored adults spawning in the shallows. Occasionally you'll see a "pet store" colored one mixed in. It was likely released at such a large size that few predators could feed on it so even with bright coloration, it survived.