How many fish are needed for aquaponics?

The general rule of thumb for identifying the number of fish you need in your system is through observance of the fish per gallon rule. Aside from this, to determine the number of fish your system requires, you have to factor in other aspects such as the shape of the tank, its surface area, water quality, and fish species.

What is the minimum amount of fish needed to start an aquaponics system?

Aquaponics adopts the best qualities of aquaculture and hydroponics in a recirculating system. For any aquaponics technique, one crucial factor practitioners consider is the amount of fish that they put inside their fish tanks. If the number of fish is off, either too low or too many, it will cause adverse effects to biotic components of the system.

So, how many fish can you put inside your aquaponics tank? Various factors influence the answer to this question. However, the size of the fish tank greatly determines the minimum number of fish that you can manage. You may also add how many crops you aim to cultivate in your grow beds.

What are the recommended fish for aquaponics?

Aquaponics generally require fish that thrive in a freshwater environment. One good reason for this is that freshwater is easier to manage than saltwater. Also, saltwater may cause corrosion to your aquaponics components over time.

Another consideration is the fish's adaptability to changing water temperature and pH range. In aquaponics, many factors may affect your water quality, and it is of utmost importance that your fish are "hardy" ones. In aquaculture, a "hardy fish" is easy to maintain and can adapt quickly to any fluctuations in the water parameters.

You also need to take into account the availability of the fish in your locality. It would be impractical to add fish species in your aquaponics tank that are not native to your region's climate. Lastly, you need to consult your local government because some cities have banned specific fish since such fish types are considered invasive.

How to solve the fish-to-water ratio in aquaponics?

When deciding on the number of fish, the best way is to consider the total weight or height of the fish instead of its total number. At this point, the fish per gallon rule applies well.

The fish per gallon rule is commonly associated with this principle: One inch of fish per gallon of water. But this rule only applies to a fish's adult size, not the size when you purchase it as a juvenile. Finally, this advice works well for most slender-bodied fish, but it is insufficient for larger wide-bodied fish.

To solve the fish-to-water ratio, you will need to understand the principle behind stocking density. The ratio of fish to tank volume is known as stocking density. It's a way to see if you have the correct number of fish in your system. The stock density is determined by several characteristics, including species, age, and size.

But the factors outlined below take precedence to determine the stocking density of your fish tanks:

The shape of the tank: Aquaponics tanks come in various shapes, including square, round, and rectangular. When filled with water, each form has its volume. The surface area is critical for CO2 and O2 exchange in the air and water. It also determines the maximum number of fish that can be kept in the system at any given moment.

Round tanks may appear unusual, yet such shapes offer several advantages compared to others with the same surface area. The circulation of water in the tank and the amount of light falling on the plants are two significant advantages. Circulation is beneficial because it allows for proper waste clearance and oxygen exchange, both necessary for keeping fish healthy.

Surface area and depth-to-volume ratio:

For a system to work well, there must be enough surface area for oxygen exchange at the top of the water and sufficient depth. It is not advisable for the fish to be reared in an environment with a low surface-to-volume ratio. For example, using a 1000-liter aquaponics tank, the number of fish is calculated as follows: (1m3) multiplied by the Density Factor (25kg/m3) divided by the weight of the fish during harvest (0.5kg).

Water quality:

The amount of fish you can stock in your system is directly proportional to the water quality in the fish tank. You can store more fish in the system if your water is good quality. If you can provide such a water feature, there will be less need for pH regulation and temperature modification.

Fish species:

Another crucial aspect that affects the stocking density is the selection of a fish species. When you decide to cultivate fish in your tanks, you should acquire the knowledge of how much care this fish will require. Note also the proper water parameters they need in order to thrive.

I recommend that you stock fish that do not elicit as much attention as their rivals. Tilapia, for example, is an ideal fish to stock in an aquaponic system since it can withstand a wide variety of pH and water temperatures. They may thrive in practically any setting as long as you supply them with sufficient food and adequate aeration.

Waste removal capacity:

Your system's waste removal capacity determines the number of fish you can place in an aquaponics system. Your fish will suffer if you do not have enough waste collection capacity. However, if your system's waste removal capacity is too high, the bacteria in your system will starve off from nutrients.

What happens if there are too many fish in your aquaponics fish tank?

Overcrowding is the direct result of too many fish in an aquaponics fish tank. This situation does not do the fish any good because it ultimately leads to many problems such as fish stress. The oxygen level also gets disrupted in an overstocked fish tank because too many fish use up the oxygen supply.

Lastly, when your fish exceeds the recommended number of species a tank can hold, a large quantity of fish waste will lead to a filthy tank.

What happens if there are too few fish in your aquaponics fish tank?

This scenario is bad for your plants. Recall that the plants' nutrients come from the fish waste produced in your fish tank. If there is a small number of fish within your aquaponics tanks, there will be fewer organic nutrients that the plants' roots can access. If this persists, you will observe that your crops are malnourished and underdeveloped.


To have an aquaponics system working well, you need to consider several factors. One of which is the number of occupants your fish tank has. The quantity of fish has an effect not only on the welfare of your desired crops but to the functionality of the entire setup. This post served as your guide in achieving the proper fish-to-water ratio, and I hope your aquaponics journey becomes more enjoyable.

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