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The Fish to Plant Ratio in Aquaponics

One of the questions an aquaponics beginner often asks in planning to build their own aquaponics system is, what is the fish to plant ratio in aquaponics? There are determined ratios between the biofilter size, planting density, and fish stocking density for aquaponics. It is challenging to operate beyond these determined ratios without risking disastrous consequences for the entire aquaponics ecosystem. However, advanced aquaponics growers are invited to experiment and adjust these ratios, depending on their needs, but it is always recommended that aquaponics beginners begin an aquaponics system following these ratios.

Why Do You Need to Know the Fish to Plants Ratio in Aquaponics?

One of the most important factors of a healthy and productive aquaponics system is ensuring that the ecosystem of the plants, fish, and bacteria is balanced at all times. This means that an aquaponics system is sized correctly to balance the plants' nutrient production from fish waste and nutrient uptake. 

Having the right fish to plants ratio is essential in maintaining balance in an aquaponics system. Here are some reasons why fish to plants ratio in aquaponics is essential:

  1. It helps keep the good water quality in the system, which is necessary for fish health.
  2. It ensures that there is enough fish to supply adequate nutrients for the plants. 
  3. Having the correct number of fish for your plants will ensure that the system is balanced, healthy, and productive.
Aquaponics System

Factors that Influence the Fish to Plants Ratio

Every aquaponics system is different in design, fish species raised, plant choice, size, and method implemented. So you need to be aware of the effect of the following factors on the growth of fish and plants. These factors will help you reach the optimum fish to plant ratio in your system. 

1. Feeding Rate Ratio

The fish to plant ratio is dependent on the feeding rate of an adequately maintained aquaponics system. Fish usually use about 80% of the food and discharge the 20% as waste. The amount of fish feed fed to the fish daily is measured per square meter of the plant growing area. 

The recommended daily fish feed rates are:

  •  For leafy green vegetables: 40–50 grams of feed per square meter per day.
  • For fruiting vegetables: 50–80 grams of feed per square meter per day.

The feeding rate ratio also depends on the following factors:

1. The type of fish.
2. The kind of fish feed (protein level)
3. Types of plants (leafy greens, tubers, or fruiting plants).
4. Type of aquaponics system.
5. Method of filtration.
6. Environmental and water quality conditions.

2. Plant Choice

Each plant has different nutrient requirements. Plants with low nutrient
requirements are lettuce, herbs, cabbage, garlic, peas, and leafy greens such as spinach, chives, basil, etc. Plants that require higher nutrient requirements are flowering and fruiting plants like tomatoes and cucumbers. 

3. Fish Choice

Your choice of fish will have a long-term impact on your aquaponics system. The most common fish species for aquaponics are tilapia, carp, goldfish, and koi. These fish species are considered hardy, stocked in higher densities, and survive in low-quality water conditions. Check the important factors to consider in choosing the best fish for your aquaponics system

4. Stocking Density

Stocking density means the number of fish you keep in your system. Remember, you cannot keep more than a specific fish in your system because they may die due to low oxygen, high nitrite levels or kill each other due to their territorial behavior. The total length of the fish is considered for stocking density rather than the number of fish. You have to manage the fish stocking density based on their size and feeding requirements. 

Fish like tilapia breed rapidly and can easily overstock your system, so it is important to know the behavior of the fish you are raising. Please read our blog about using tilapia in aquaponics

5. Type of System

The size and type of aquaponics setup implemented to tell the system's ability to turn fish waste into nitrates. The more surface area your system has, the more fish you can raise as they harbor the bacterial colony that is important in converting fish waste into nutrients for the plants. 

Fish Stocking Density in Aquaponics

Deciding Your Feeding Ratio

There is a determined ratio in aquaponics, but it's just a recommended ratio. Only you can decide the right ratio for your system based on the factors mentioned above. However, an aquaponics beginner needs to follow the rule of thumbto avoid mistakes that can lead to system failure while you're still learning the ins and outs of aquaponics. Once you've gained enough knowledge, you can experiment with your system. 

As a general rule, it is recommended that the fish tank volume should be equal to the grow bed volume, which makes the grow bed to fish tank ratio approximately equal to 1:1. The most directly related factor in the fish to plant ratio is the feeding rate. If you have 100 square meters of growing area for plants, you need to input 7-10kg feed to your fish. You can manipulate the fish tank, tank volume, and stocking densities to achieve your target ratio. This ratio can also be determined through your growing method. 

Here is the feeding rate to your growing method:

  • Raft or Deep Water Culture60-100 g of fish feed per day per square meter growing area.
  • Grow beds: 15-40 g of fish feed per day per square meter of growing space.
  • NFT: 15-25 g of fish feed per day per square meter of growing area.

You have to minimize solid discharge through the solid filtration system. Solid discharges will cause a less solid breakdown, which will lead to fewer nutrients available for the plants. You can use mineralization to convert fish waste into usable nutrients for the plants.

The ratio can also be determined in gallons per cubic foot (6 gallons of fish tank to every cubic foot of grow bed). In bigger aquaponics systems, you can increase this ratio to 1:3 or 1:4 depending on fish density and water flow rate. Fast water movement and abundant aeration also enable bigger systems to stock fish to 1 fish per 8-10 liters of water. The important thing to remember is, you have to determine the ratio of your aquaponics system based on the factors mentioned above. 

Final Say on Aquaponics Fish to Plant Ratio

The feed rate ratios will provide a balanced ecosystem for the fish, plants, and bacteria, provided there is adequate biofiltration. It is important to note that the feed rate ratio is only a guide to balancing an aquaponic unit, as other variables may have larger impacts at different stages in the season, such as seasonal changes in water temperature. Use this ratio when designing and starting your own aquaponic system to ensure you will not make any mistakes at the beginning of your aquaponics journey. Once your system is mature and you know the ins and outs of aquaponics, you can adjust these ratios to suit your needs. 

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