I just remember a small 1/8 acre pond where I grew up in NJ. It had tons of goldfish and nothing else for years. A new person bought the house and added BG and LMB. Withing 3-4 years, there was about three goldfish left that were huge - 16-18 inches and a LMB of the same size would follow one of them around like they were buddies. I think it was just a massacre at first (when LMB were added) due to their color and slow swimming. Then, any babies born would just get eaten (probably by BG and LMB) and eventually only a few large goldfish adults were left - i.e. they probably spawned each year, but all babies were eaten right away. This is all in a pond where goldfish were established. My cousin has a 2 acre pond (with BG and LMB) and has tried adding goldfish many times over the years and we have never seen one last for more than 52 seconds. We used a blocking net one time to "grow" them out and came back a week later to find a 8 inch LMB swimming around (fat) and no goldfish left.
