How Many Fish Should You Have In An Aquaponics System?

Aquaponics is a system that combines the best aspects of hydroponics and aquaculture to create an efficient, sustainable way for growing plants and fish together. While it is a great way to grow your food, it’s also an excellent way to have fish as part of your diet. You can also raise them for commercial purposes. The answer to the question “How many fish should you have in an Aquaponics system?” is subjective.

The number of fish living in your aquaponics system is important because they will be living there for their entire lives in order to be a sustainable population. If you have too many fish, they may not have enough space to be comfortable and become stressed. If you have too few fish, then the system will not be efficient because the bacteria in the system would need more time to convert waste into nitrates for your plants.

how aquaponics works

So what is a safe number of fish in your aquaponics fish tank? The answer to the question is based on the size of your tank and some other factors. Keep reading for more information.

Let’s get started.

Water: Fish Ratio

When deciding the number of fish, it is recommended to consider the total fish weight or height and not the number.

This is where the fish per gallon rule comes in. Consider the following example:

Size of fish Amount of water Size of fish you can raise
Smaller fish species
1 gallon of water
Up to an inch

However, the above is relevant only for smaller aquaponics tanks and does not work for fish that can grow large in size. With time, a fish will grow in height, length, and width. And hence, the weight and volume of a say 10 inches fish will be more than an inch of fish. Note that one can determine the density in pounds.

Size of fish Amount of water Size of fish you can raise
Larger fish species
5 -10 gallons of water
1 lb of fish

Note: 1 gallon of water is 231 cubic inches.

What Is Stocking Density? Why Is It Important?

Stocking density is the measurement of fish to tank volume. It is a way to determine if your system has the right amount of fish in it. The density of the stock is dependent on various factors, including species, age, and size. It’s always a good idea to have some fish that are at least large enough to eat any other fish that may decide to dine in your aquaponics system.
Stocking density is important because it tells you how much food to feed your system and how much room the fish have to grow.

The four factors that define proper stocking density are the shape of the tank, surface area and depth to volume ratio, waste removal capacity, and water quality. These will be discussed elaborately throughout this article.

When determining how many fish should go into a system, it is essential to consider all of these factors.

1. Shape of the tank

An aquaponics tank can be square, circular or rectangular. Each shape has its volume when filled with water. The surface area is important for the exchange of CO2 and O2 into the air and water. It also dictates how many fish can be in the system at one time. The more surface area there is per gallon, the less fish can go in because the food will spread over a large area. The calculation for a surface area is length x width, divided by 2.

Round tanks seem odd, but they provide many benefits at higher densities than other shapes with the same surface area. Two main benefits are the circulation of water in the tank and the amount of light that falls on the plants. Circulation is beneficial as it allows for proper waste removal and oxygen exchange which keeps fish healthy. When stocking density is considered, you can control the amount of waste produced by your fish and the space they need to grow.

aquaponics fish

2. Surface Area and Depth to Volume Ratio

For a system to work efficiently, there must be enough surface area for oxygen exchange at the top for your water, as well as an adequate amount of depth so that your fish can spend time away from predators.

As the amount of surface area increases, oxygen exchange becomes more efficient. The higher the surface-to-volume ratio, the easier it will be for oxygen exchange and waste removal. This is important because it will make the fish happier and less stressed. A happy fish is a healthy fish. Fish should never be in an environment with a poor surface-to-volume ratio.

For example, with an aquaponics tank water volume of 1000 litres, you work out the number of fish like this: (1m3) multiplied by the Density Factor (25kg/m3) divided by the weight of fish at harvest (0.5kg).

3. Waste Removal Capacity

The waste removal capacity of the aquaponics system determines how many fish you can put in your system. It’s one of the most important things to consider when determining how many fish to stock your system with. If you do not have enough waste removal capacity, your fish will die.

However, if your system has too big a waste removal capacity, the bacteria in your system may starve for nutrients. Fish naturally produce ammonia, and their poo is full of solid matter as well. As this matter decomposes in the water, it produces toxic compounds (nitrite and nitrate). The waste removal capacity is the amount of ammonia and solid waste that the bacteria can break down. It also allows your fish to live in an environment with a proper pH level.

4. Water Quality

The quality of water supplied to your system directly correlates with how many fish you can stock into the system. If your water is of high quality, you can stock more fish in the system. This is because there will be less need for pH control and temperature adjustment.

If you have low water quality (lots of chemicals or sediments), more care needs to be taken to ensure that the fish are well cared for and cared for. As you increase the density of the fish in an aquaponics system, you have to work harder to keep them healthy and happy. This means that you have to do daily checks of the tank and water parameters.

5. Fish Species

Picking a fish species is an important part of stocking density. You should be aware of how much care your fish will need before making a purchase and consider the environment they are going in to properly stock it.

Stock fish that require less care than their counterparts. For example, Tilapia is an excellent fish to stock in an aquaponic system because they tolerate a wide range of pH levels and water temperatures. They will do well in almost any environment as long as there is enough food for them and the aeration is suitable.

best fish for aquaponics

6. Temperature

Temperature is a significant factor for all life on earth. Fish are no exception. All fish species are comfortable in specific temperature ranges and will thrive if kept within that range.

There is a myth that fish are not warm-blooded creatures and that water temperature does not affect them. In reality, water temperature is critical to the health and well-being of fish. Letting fish live in suboptimal temperatures will result in a weaker immune system and stress on their bodies.

The ability to control water temperature is essential for an aquaponic system. The ability to keep the water at a habitable temperature will allow you to stock a higher density of fish in your system without having to worry about the fish being freezing or boiling alive.

If you are in a colder climate and cannot control your water temperature, it is best to stock fewer fish than recommended. If you are in warmer weather, then you should be able to stock more fish because of your ability to control temperature ranges. A good rule of thumb for fish stocking species is 1″ or 5 gallons per degree Fahrenheit.

Best Fish For An Aquaponics System

Now that you know the amount of fish you should grow, let us tell you about the best fish to grow in an aquaponics system. These include:

  • Tilapia.
  • Catfish
  • Carp
  • Pacu
  • Koi
  • Goldfish
  • And some ornamental fish such as tetras, guppies, mollies, swordfish, angelfish.

Wrapping Up

It is best to start with one or two fish in your system. Some people like to start small and then add more as they get the hang of things, while others prefer a larger initial investment so that their first crop can offset the cost. Either way is fine, but you might want to consult an expert before making any final decisions about how many fish are best for your Aquaponics system.

Suppose you want to maximize your production potential or have other goals besides sustainability. In that case, larger fish will be better suited for your needs as they produce more waste, leading to higher nutrient concentrations in your water supply. For instance, goldfish grow much faster than tilapia and need less space (and therefore take up fewer resources), but they also require three times as much food per pound of fish.

Consider your goal and decide about the amount of fish in an aquaponics system accordingly!

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Welcome to The Aquaponics Guide

Hello! We are the Johnsons and the faces of The Aquaponics Guide. We have been avid gardeners for many years and growing our own food is one of our key priorities. We have found sustainable Aquaponics farming to be a life changer, which is the reason we have created The Aquaponics Guide. 

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