Koi Fish for Aquaponics: What You Need to Know

Excited about starting your new aquaponics system - but not sure which fish to use? 

Don’t worry. 

If you are wondering if you can use koi fish in an aquaponics system, you’ve come to the right place. 

Aquaponics, as you know, is a creative method of agriculture that utilizes fish waste as a natural fertilizer for plants in a cyclic ecosystem. 

The plants and beneficial bacteria in the water remove nitrogenous compounds like ammonia, helping create a healthy atmosphere for your fish. 

Koi, an ornamental type of carp, thrive in aquaponics systems. Even though they aren’t technically edible, they live an incredibly long time and are some of the hardiest fish you will find. 

Here’s everything you need to know about keeping koi fish in an aquaponic system.

Temperature

The major benefit of using koi in an aquaponics system is that they are highly tolerant of a wide range of temperatures. 

Most do best in water that ranges from 35 to 50 degrees Fahrenheit, although they can survive outside of this range, too. 

This means you won’t need to heat the water to keep your fish healthy. 

Feeding

They aren’t fussy eaters, either. They will eat natural substances like algae and food waste, with very little fish food required.

In fact, they will eat practically anything you give them, from plant matter to green vegetables. 

Koi are unique feeders in that they have long intestines. They can extract more nutrients out of their food than almost any other type of fish. 

This lowers your feeding costs and maximizes your ability to look after and care for your fish. 

When you’re operating an aquaponics system, you’ll have enough work to do when it comes to maintaining water parameters like nitrites, ammonia, pH, nitrates, and temperature - if you can cross at least one item off your to-do list, you’ll be all the more grateful for it.

Tolerance

Koi are also resilient to disease. They can handle fluctuations in water quality and require minimal levels of care. 

They are some of the best fish at creating nutrients in an aquaponics system, such as ammonia, magnesium, and potassium - all of which are required for healthy plant growth. 

Edibility

As with any aquaponics fish species, there are disadvantages to selecting koi. One of the biggest issues is that koi are not typically used as food sources. 

For most people, the major draw of an aquaponics system is that it can provide two sources of food: fish and plants (usually vegetables).

However, koi don’t really check off that first box. You may be able to raise them in your pond for the purpose of selling them to collectors later, but you’ll reduce the overall potential for harvest from your system.

Cost

Also, koi are not the cheapest fish you can buy. They’re not the most expensive, either, but it’s important to keep in mind that mature koi can potentially cost thousands of dollars. 

Investing in younger koi is a great way to save money, and you can always sell your mature koi back to collectors later on.

Koi are large fish, and they are also long-lived fish. They can live up to thirty years in captivity and grow more than three feet in length! 

As your fish grow larger, they are going to need more space to thrive. The more fish you have, the more magnified these spatial needs become. 

Ideally, you should have a tank or pond that is at least ten feet deep and contains more than 1000 gallons of water. This will support a population of five or six mature koi. 

With that said, it is not recommended that you start your system off with fully grown, mature fish. Instead, start with small fish. 

This will let your fish get acclimated to the system and also keep your aquaponics system healthy and functional.

Before you start a koi aquaponics system, think carefully about the design. If you’ve raised koi in a pond before, you’ll need to make a few adjustments so that you also have a thriving aquaponics set-up. 

Zoning Compliance

First, remember that some areas have regulations in place related to aquaponics in ground ponds. You may have to fill out forms or pay some licensing fees - it’s important to consult a professional or a zoning authority to make sure you comply. 

Location

Next, consider where exactly you will put your koi pond. It needs to be relatively large, as koi grow up to 36 inches long and need at least 200 gallons to thrive. 

Your location also needs to be easy to access and provide room for you to install plumbing and electrical systems, too. 

Pond Size

Paradoxically, larger ponds are much easier to care for. They tend to be more self-regulating, so if you have space, bigger is definitely better when it comes to a koi aquaponics system. 

Plus, a deeper pond will stay warmer during colder weather, helping to protect your fish. 

A koi aquaponics system almost always needs to be located outdoors. Therefore, water levels may fluctuate. You might need to add water on a regular basis, so locating your koi pond near a water source is a smart idea. 

Protection

Finally, predators are not out of the question when it comes to koi ponds. You may need to install some kind of fencing or pond covers to keep hungry birds and mammals away from your fish.

Containment

When you first set up an aquaponics system, your first step will be to establish a tank. You can use a rigid pond liner, an old IBC tote, or any other large container for this purpose. 

You can also use an established pond. 

Season

Try to start your system in the spring or summer, which is the natural time to begin most gardening endeavors anyway. Warmer temperatures will help your koi flourish. 

Your koi will need to be fed several small meals throughout the day to produce more waste. In the winter, they will only need to eat once a day since their metabolisms slow down. 

Therefore, they will produce less waste and have fewer nutrients to cycle back to your plants. 

In the warmer months, you may need to add oxygen back to the water. Cold water naturally holds more oxygen, and too little oxygen can cause health issues for your koi. 

Filtration

As your fish get larger, they will produce more waste. You will need to keep an eye on waste production and the levels in your pond. 

Although you don’t need an expensive filtration system when you are just getting started, it may useful to upgrade to a more efficient filter after your fish have matured a bit. 

You can also expand your grow bed, which will allow you to make the best use of these excess nutrients.

Absolutely. Many people use existing koi ponds for their new aquaponics systems - after all, you’ll already have half the work done. 

Your pond is already built and your koi are already established. You’ll just need to set the pond up so you can connect your grow beds. 

The key to using an existing pond is to establish a better routine of maintenance. You will need to test the water more often for things like temperature, ammonia levels, and pH. 

While koi can tolerate some fluctuations, your plants may or may not be as good at doing so. 

You may need to drain the water and add fresh water from time to time, too. Monitoring algae levels will be even more important when you are working on an aquaponics system in your koi pond.

pH Levels

Koi are a bit different from most other aquaponics fish species in that they can tolerate a wide pH range. 

Temperature

They’re also tolerant of temperatures from 35 to 85 degrees, making them some of the most resilient fish species around. 

However, you do need to keep in mind that they grow quite large, and they aren’t as skilled at eating algae as some other fish species. 

Therefore, you may still need to clean your system from time to time. 

New Fish

When you’re setting up your aquaponics system, remember to quarantine any new individuals before adding them to the tank. 

Even aquatic plants can harbor snail eggs or harmful organisms that can throw the balance of your tank off - or even introduce disease. 

Add koi gradually, as adding all of your fish at once can spike ammonia levels, creating a dangerous environment for both your fish and your plants.

Enjoy

And most importantly? Remember to have fun! Aquaponics is a fun hobby that can be incredibly beneficial for you, the plants, and the fish. 

Experimentation is key - don’t be afraid to try new things until you find the aquaponics system that works best for you.