The Ugly Truth – Will Koi Fish Eat Other Fish?

Koi are basically giant, water-breathing pigs.

I just got off an exhausting nine-hour shift cleaning filters, my hands are cracked, and I am staring at my screen because I keep getting this exact same question. People always ask me, ” Will Koi fish eat other fish when they set up their first outdoor water feature.

If a fish fits inside a koi’s mouth, it is legally food. They do not care if you spent twenty bucks on that beautiful little fancy guppy. They are opportunistic omnivores that constantly forage around the bottom of your koi pond, looking for anything they can suck up and crush.

The Mistake That Still Haunts Me

Back in 2017, I thought I was incredibly smart when I tossed a dozen tiny rosy red minnows into my main display vat to control mosquitoes. It was a warm Tuesday afternoon, and I felt so proud of my natural pest control idea. The very next morning, I walked out with my coffee and watched my prized 24-inch Kohaku casually inhale three of those minnows in one massive slurp.

I literally yelled at a fish. I had to drain half the tank to net out the surviving minnows before they all became expensive snacks. Will Koi fish eat other fish?

Yeah, they will aggressively hunt them down if they are hungry enough.

Why People Get This Totally Wrong

Here is my highly unpopular opinion that always gets me roasted by the old guys at the fish club. You should never mix different species in a high-end setup. Period.

People think that because koi lack a real stomach, they just lazily munch on algae all day. They ignore the fact that these animals grow incredibly fast and will absolutely devour smaller tankmates to fuel that growth. Proper pond fish care means accepting that big fish eat little fish.

Stop Feeding Them Your Other Pets

Feeding koi a properly formulated diet is the only way to stop them from hunting their neighbors. A well-fed fish might ignore a smaller buddy, but the second they get hungry, that little guy looks exactly like lunch. So, will Koi fish eat other fish if you skip a few meals?

Without a doubt. Seriously. Keep your population size-matched so nobody fits in anyone else’s mouth.

Stop reading this and go outside right now to check the size difference between the largest and smallest fish in your yard. If the little one can fit inside the big one’s mouth, grab a net and separate them in the next ten minutes. Do not wait until you wake up to a missing pet tomorrow morning.