We all already know that aquaponics is a method where the plants utilized the wastes produced by the fish as nutrients or food sources. It means that the fish are fed, and the plants use their wastes as a source of nutrients for them to thrive in the system.
For a sustainable aquaponics system, the balance between the amount of fish waste produced, and the number of nutrients needed for plant growth should be met. To achieve this, you need to have proper fish to plant ratio in your system. In this article, we will discuss the right fish to plant ratio in aquaponics and the factors involved in figuring out what is the right fish to plant ratio in your aquaponics system.
Nutrients for the Plants
In aquaponics, the primary source of nutrients for plant growth are the wastes produced by the fish. So the number of plants that can be grown in the system is related to the amount of fish feed that enters the system. Therefore, there should be enough fish in the system, and these fish must be fed enough to supply the adequate amount of nutrients needed for the plants.
Using Aquaponics Ratio
There are several important factors to consider in figuring out what the right fish to plant ratio is in aquaponics. There is no exact fish to plant ratio, and every aquaponics system is different, but this ratio will guide and help you find the best balance for your aquaponics system.
1. Feeding Rate
The fish to plant ratio depends on the feeding rate in an adequately maintained aquaponics system. Fish use about 80% of the food they consume and excrete 20% as waste.
The amount of feed added to your aquaponics system daily is considered per square meter of plants growing area. This ratio also depends on the feed used and the plants grown in the system; fruiting vegetables requires about one-third more nutrients that leafy greens to thrive. (1)
Daily fish feed by plant type
- Leafy Greens: 40 – 50 g of fish per square meter
- Fruiting Vegetables: 50 – 80 g of fish per square meter
This fish feed ratio is to ensure that plants have adequate nutrients in the system. However, this ratio will only be used as a guideline, as the feeding rate ratio depends on factors such as grow beds, type of plants, and fish species.
To ensure the success of your system, feed your fish with the best fish food that has all the nutrients for your fish and plants’ optimum growth.
2. Stocking Density
Stocking density is the amount of fish to keep in your system. It is best to start with a smaller number of fish. You can adjust to the number of fish on your system once you are comfortable with the monitoring and regulating the water quality of your system by changing your feeding frequency.
To keep things simple, stick to a lower stocking density as higher density requires more aeration and filtration. An overstock system can also kill the fish because of low dissolved oxygen, high nitrate level, or fish territorial behavior. The stocking density in aquaponics is based on the length of the fish, not the number of the fish. The recommended stocking density is 10-20 kg of fish per 1000 Litre of water. (1)
Fish Stocking Density Table for Small Scale Aquaponics System.
To keep your system balanced, you also need to make maintenance checks such as; daily monitoring of the fish and plants, and water testing.
3. Fish Species
Fish play a vital role in the aquaponics system as they are the source of natural fertilizer for the plants. There are many types of fish that you can raise in your aquaponics system, but it is essential to select fish species that will survive and thrive in your aquaponics system. In choosing fish to grow in your aquaponics system, it is essential to consider these important factors.
- Water Temperature: Choose a fish that will thrive in your climate and water temperature. If you live in colder weather, choose a fish like the trout, and if you live in a warm climate, you choose tilapia. Selecting a fish that thrive well in your climate is necessary for the easy maintenance of your system, and it could also help you save some electricity. (2)
- Fish and Maintenance Difficulty: Some fish are hardy and need little care while other fish are sensitive. Choose a hardy fish that is easy to maintain and immune to diseases. Tilapia and Koi are examples of hardy fish and great for beginners in aquaponics.(2)
- Breeding Habits: Some fish, like tilapia, reproduce quickly and quietly. You need to monitor their stocking density during the spawning season. You may also need to have a separate tank for fish breeding and to keep the young alive and healthy.(2)
Keeping your fish healthy is essential in keeping your system balanced.
4. Plants Choice
The important thing you need to consider in choosing plants to grow in your aquaponics system is the nutrient needs of your plants. As a rule of thumb, choose plants and fish that have a similar temperature, and pH level needs to grow in your system. The closer they match, the better they will grow.
Making the right choice in plants to grow in your system is essential to the success of your aquaponics system. Unhealthy plants affect the purity of the water that can be harmful to the fish. Different plants have different needs. Green leafy vegetables like lettuce, cabbage, spinach, basil, etc. require low to medium nutritional needs. While, fruiting and flowering plants like tomatoes and cucumbers have higher nutritional requirements. (3)
5. Type of Aquaponics System
A new aquaponics system needs to be “cycled” first before you can start planting plants in your system. Cycling is a process of establishing beneficial bacteria into the system so that the bacteria can convert fish waste (ammonia) into nutrients for the plants (nitrates). Bacteria are the third element of aquaponics that serve as the bridge that connects fish waste into nutrients for the plants.
It is tricky to maintain fish to plant ratio in a newly built aquaponics system. So it is the best practice to start with a smaller amount of fish, then increase their population once your plants grow to ensure that the fish are providing enough nutrients for the plants.
The type of your aquaponics set up is also important because it tells of your system’s ability to turn fish waste into the plant’s food. The more surface area you have in your grow bed, the more fish you can grow.
So what is the best fish to plant ratio?
There is no one set fish to plant ratio. It depends on your feeding rate, the the type of fish, the the variety of plants you’re growing, and type of aquaponics system you are using. As a guideline, the best fish to plant ratio is for leafy greens: 40 to 50 g of fish per square meter and for flowering or fruiting plants 50 to 80 g of fish feed per square meter.
In conclusion, determine the ratio of your aquaponics system based on the factors and guidelines listed. Starting a new aquaponics system is trial and error. So start small and don’t be afraid to experiment until you achieve what is the best ratio for your aquaponics system.