Goldfish are fun fish to watch swimming around your tank or pond. Still, they don’t come in a lot of colors.
Are you looking for a fish that’s a bit more majestic and comes in all kinds of varieties and colors? Have you been thinking about adding koi to your goldfish setup?
Can koi and goldfish live together?
In short — yes — but you need to have the right setup to be successful. Koi will live peacefully with goldfish, but they’re more difficult to take care of.
Koi and goldfish can live together in harmony. They are both peaceful fish with the same water requirements.
Where this gets difficult, is making sure that you have the perfect setup for your koi. Koi grow much larger than goldfish, and they’re harder to care for.
Goldfish are a selectively bred mutation of the Prussian carp, Carassius gibel. Breeding began over 1,000 years ago in China where people kept them as pets as a status symbol.
They originated in the eastern area of China from the south of Bejing to the north of Macau.
About Koi Fish
Koi are also a selectively bred mutation of the common carp, Cyprinus carpio. Koi originate from parts of eastern Asia and China in the Black, Caspian, and Aral seas.
The popularity of koi began to explode about 1914. This is when very colorful varieties went on display at an exposition in Tokyo.
Fish Pond Requirements
Goldfish and koi have many of the same water requirements. The issue is making sure you choose an enclosure large enough to house both species.
Koi grow much larger than goldfish — some koi can grow up to 3 ft (0.9 m). But, the largest goldfish will only grow up to 14 in (35 cm).
Don’t House Your Koi In An Aquarium
While most goldfish can live in a large tank, koi can’t. You should never attempt to keep full-grown koi in a personal indoor tank.
If your koi are babies, you can keep them in a large aquarium tank temporarily. The tank should be at least 50 gallons.
Some hobbyists will do this while they’re waiting for their new pond to cycle. But, you should never keep koi in a home aquarium tank after they’ve surpassed 6 in (15 cm) in length.
To live happily, you need to have a pond that is at least 1,000 gallons. A single koi needs at least 200-300 gallons.
Koi are social fish, so you need to keep several in a single pond. A 1,000-gallon pond will allow you to house 3-5 koi at once. You should keep at least 3 koi together. Ideally, you will keep even more than that.
Goldfish are much smaller and don’t need as much room. You will need at least 50 gallons for each goldfish you add to the pond. This is besides the volume you keep for your koi.
The pond should be at least 6-8 ft (1.8-2.4 m) in length to give your koi enough space to swim around.
Also, some part of the pond needs to be at least 3-4 ft (0.9-1.2 m) to help the fish overwinter. The deeper the water, the warmer the water will be. This helps your koi when the surface of the water freezes over.
Koi and goldfish have almost identical water needs, so it isn’t difficult to house them together. Their basic water parameters should look like this:
- Ammonia: 0ppm
- Nitrites: 0ppm
- Nitrates: <40ppm
Ideally, you should keep the pH between 7.2-7.5. Still, if the pH fluctuates a bit, your fish will be fine. Koi and goldfish can survive in a pH between 6.5-8.0.
Most people want to keep plants in their pond — it adds to the aesthetic after all. But, goldfish and koi are both known to rip up plants and eat them. Plants provide a great food source for fish. Still, it can be frustrating having your plants destroyed.
Sturdier plants include water hyacinth, water lettuce, and water smartweed.
Will Koi Kill Goldfish?
If you plan to keep goldfish and koi together, make sure you choose fish that are about the same size. Avoid getting exceptionally large koi and housing them with your goldfish.
If your koi grow too large, you may have to separate them.
Koi Fish Eat Goldfish
While koi and goldfish are peaceful species, they are opportunistic omnivores. They will eat anything that will fit in their mouth. If a goldfish is too small, a koi will eat them. Yes, koi fish eat goldfish.
How To Handle The Changing Seasons
Both koi and goldfish are cold tolerant, so you can keep them in an outside pond year-round. Still, there are a few things you should do to keep them safe throughout the changing seasons.
Spring & Summer
The most important thing to keep an eye on during the summer months is the oxygen levels. Warm water doesn’t hold oxygen as well as cold water. If your fish aren’t receiving enough oxygen, they may suffer and even die.
To learn about how much oxygen your goldfish need, check out this article.
Fall & Winter
These fish are cold tolerant, but they won’t survive in temperatures below freezing. If you live in a region that freezes, you’ll need to buy pond heaters.
During the fall, make sure to feed your fish more than usual. This helps their body store up energy that they’ll need over winter. Once the winter months hit, you should begin feeding your fish less than you do throughout the rest of the year.
During the fall, remove any plants that are dead or will die over the winter. Dead plants in and around the water will cause an ammonia spike in your pond.
Can Koi and Goldfish Eat The Same Food?
Koi and goldfish are both omnivores that eat many of the same things. The main thing to worry about is that your koi aren’t stealing all the food from the goldfish. You need to make sure that you’re adding enough food for all your fish.
Your fish’s diet should consist mainly of a high-quality flake diet. For goldfish and koi food, TetraPond Variety Blend Fish Food is one of the best options. Check the price here
As we mentioned earlier, your fish need a good assortment of plant matter as well. If you don’t want them eating your plants, consider giving them leaves of lettuce.
You should also give them supplemental feedings of live food. This food is a good source of protein for your fish. It also provides them with wonderful enrichment as they look about the tank for their meal. Some good options include Rosey Red minnows or guppies.
Do Koi and Goldfish Interbreed?
Yes, it is possible for goldfish and koi to interbreed, although it’s not all that common. It’s more likely that your goldfish will breed with one another.
Still, if your goldfish and koi do interbreed, the offspring produced will be sterile. Also, it’s likely that the adults will eat the eggs or baby koi fry before they ever even make it to adulthood.
Goldfish and koi are both colorful, peaceful fish that can coexist. It is entirely possible to house the two species together, and many people do it every year.
The main thing you need to worry about is that you’re providing your fish with enough space. Koi grow far larger than goldfish, so make sure you set up a large pond for them!