Thats why goldfish are illegal to use as bait, they establish themselves and compete with natives.

Years ago, I was shocking a lake up near the Oregon border. I started shocking these odd fish. I hadnt been in Cali for that long, so I just figured they were some kind of weird west coast carp. Turns out they were all goldfish, the bronze/gold variety. And they were big, like 3-5 pounds. Pretty cool. But, they were there because people were using them for bait.