Koi fish are known to eat goldfish, especially smaller ones. Koi are opportunistic feeders and have been known to prey on smaller fish in their environment, including goldfish. This is something to consider if you have a pond with both koi and goldfish.
It is important to note that not all goldfish are at risk of being eaten by koi. The smaller and more delicate varieties of goldfish, such as fancy goldfish, are more vulnerable to being preyed upon by koi. On the other hand, comet goldfish, which are slimmer and faster, tend to have a better chance of avoiding being eaten by koi.
If you have both koi and goldfish in your pond and want to minimize the risk of the goldfish being eaten, it is recommended to choose comet goldfish as they are more able to defend themselves and swim away from the larger koi. These fish are also more agile and faster, making it difficult for koi to catch them.
Another consideration to keep in mind when keeping koi and goldfish together is the issue of overstocking. Goldfish are known to breed prolifically, and if you have too many goldfish in your pond, it can lead to overcrowding and potential health problems for both the goldfish and koi. It is important to monitor the population of both species and ensure that the pond is not overpopulated.
In my personal experience, I have witnessed koi fish eating smaller goldfish in a pond. I had a pond with both koi and fancy goldfish, and despite my efforts to provide ample hiding spaces and vegetation for the goldfish, some of them still ended up being eaten by the koi. This prompted me to rehome the goldfish and keep only the comet goldfish with the koi, as they were better able to coexist.
To summarize, koi fish are known to eat goldfish, particularly smaller and more delicate varieties. If you want to keep both koi and goldfish in the same pond, it is advisable to choose comet goldfish as they have a better chance of avoiding predation. Additionally, it is important to monitor the population and avoid overstocking the pond to ensure the health and well-being of both species.