A very common question is: ”how many fish should I put in my aquaponics setup?” and this is what
we will develop in this video.
When you design an aquaponics setup you must keep some numbers and ratio in mind. Indeed, there is a clear limit to the quantity of fish that your aquaponics setup can hold. The more fish biomass you will keep into your aquaponics setup and the more fish food you will have to feed them. As a result, more ammonia will be released. Therefore, the quantity of fish able to live into the aquaponics ecosystem is directly dependent on the quantity of bacteria able to transform the ammonia into nitrite and nitrate.
Bacteria will determine how many fish you can keep in your aquaponics system
The quantity of bacteria is directly dependent on the grow-bed volume. As well as the quality of media selected. Indeed, the bacteria population will be limited by the surface they have to develop on. In this video we see that the largest the grow-bed volume is and the more fish you are able to stock into your aquaponics setup. If you have enough bacteria, they will transform all nitrogen into nitrate. The plants will be able to consume the nitrate. However, if you don’t have enough plants into your aquaponics setup, the nitrate will slowly build-up.
Nitrate limit
Nitrate is not as toxic for the fish as ammonia and nitrite. But it is a good thing to keep it below 40 ppm. If you see the concentration over this number you can simply use some water from your aquaponics system to water your classic garden. As you will top-up your system with some new water, it will dilute the nitrate concentration.
Ratio fish biomass / Grow-bed volume
How many fish for aquaponics
So how to calculate the maximum quantity of fish to put into your aquaponics setup? Well there is not straight and easy calculation. The bacteria have different yields depending on the water pH, the temperature of the water, the quantity of oxygen available… However, we like to give a rough maximum ratio of 1 kg of fish per 50 liters of grow-bed volume. This is a maximum limit for the most efficient media. Therefore, I recommend to always remain below. In other words, this is not a target but a maximum limit to stay under.
Is there a minimum quantity?
The other question is: “what is the minimum quantity of fish required for my aquaponics setup?”. Indeed, the plants food “Nitrate” quantity generated by the aquaponics system will be directly dependent on the quantity of fish biomass into the fish tank. When you begin your aquaponics setup, you generally add fingerlings fish after cycling the system. The total biomass of those fish (average weight x number of fish) is generally fairly low. Meanwhile, the plants and vegetables population is also young (especially if you grow your plants from seeds). So in this case the system is somehow balanced. If you add a significant quantity of plants from the garden shop at the beginning, you may not generate enough nitrate to feed them. In this case we have 2 main options:
The first and most common one is to add more fingerlings and to sell them later on when the total
fish biomass get closer to the limits of the system.
The other option is to add some fertilizer directly into your system (some people add Seasol to their Aquaponics water).
You will probably be interested to discover Jonathan’s six steps to build and manage an Aquaponics system. Click here to access for free! Thanks and good reading 🙂
