How Many Fish Do I Need To Grow In An Aquaponic System?


aquaponic system fish

Aquaponics is an innovative and sustainable solution to combine fish and plant cultivation in a symbiotic recirculation system. This bio-integrated system uses aquaculture waste to grow plants hydroponically. Aquaponics is done with a wide variety of aquatic animal species, plants and system designs. Depending on various factors, different types of fish and plant species are used.

The aquaponic system increases water productivity by producing fish and plants without the need for water or fertilizers. To ensure a sustainable aquaponics system, you should know the number of fish to store in your tank and you must also have a good fish-to-plant ratio.

How many fish do I need to grow in an aquaponic system?

The number of fish you want to grow or the number of fish you need comes first on your plate. At home, this depends on how many fish you want each week and how many people you feed. If you are trying to grow your business, it will be calculated based on the amount of fish you can sell per year and the cost of production. For this example, we will use 50 fish.

The next thing to consider is how big you want your fish to grow. Suppose you like to eat fish of 500 grams each. A 500-gram fish is the general market size for many species as they are considered “plate size”. Some are smaller, some are bigger, but you have a choice so it’s up to you. When you grow fish to sell, the size depends on what your customers want to buy.

Find out how much water your tank is using

If you are working with a known tank volume, for example, 1000 litres. It is important to work with the actual volume of water in the tank when it is running. Don’t think that a 1000 litres IBC is a 1000 litres fish tank. If you cut it off and then leave the water below the 100mm top your IBC will only hold 850 litres of water.

With the water volume in the 1000 litres tank, you can calculates the amount of fish in this way: (1m3) multiplied by the density factor (25 kg / m3) divided by the weight of the fish at harvest (0.5 kg) gives you the amount of fish to save with. This example = 50 fish.

Working with fish number

The number of fish (100) multiplied by the catch weight of the fish (0.5) divided by the density factor (25 kg / m3). You need at least 2m3 or 2000 litres; more is better.

Keep your fish in the best possible environment and they will always produce a beautiful product.

Deciding your feeding ratio

There is no perfect ratio of fish to plants in aquaponics. It is different for each cultivation technique and type of cultivation that you are going to use.

Use a feeding rate applicable to your growing technique:

  • Grow beds – 15-40 grams of feed per day per square meter of growing area
  • NFT – 15-25 grams of feed per day per square meter of growing area
  • Deepwater cultivation (DWC) – 60 -100 grams of feed per day per square meter of cultivation area

Yоu nееd tо minimize solids dіѕсhаrgе thrоugh a solids fіltrаtіоn ѕуѕtеm. Solids discharge means less decomposition of solids, which will lead to less availability of nutrients for plants. You can use mineralization to convert fish waste into usable nutrients.

1. Fish to plant ratio in growbeds

I will explain this with a simple example; let’s assume you are using a growbeds, you need to adjust the size of your grow beds so that they can process your fish waste completely.

Let’s say you want to have three grow beds (each 4ft x 4ft) with a recommended depth of 12 inches and hydro ton as the growing medium.

You will need to feed your fish 15-40 grams of fish food per day per square meter.

The three grow beds have a combined growing area of ​​3 square meters.

You need to feed your fish 45 to 120 grams per day.

Use 45 grams if you are not discharging solid fish waste and 120 grams if you are discharging solid waste into your garden.

Using this ratio will keep your leafy greens from showing nutrient deficiencies. Growing more food-hungry plants, such as tomatoes, requires more fish food (40 grams).

Now you have to figure out how much fish is going to eat these 45 grams of fish food per day.

Tilapia is known for growing quickly and having a good feed conversion ratio (FCR). They have a conversion rate of 2 which means they need two pounds of fish food to grow to one pound. They will grow from fingerling to a pound in 6 months.

45 grams x 182 days (6 months) = 8,190 grams. You would need 8,190 grams of fish food (8.19 kg) to grow tilapia in six months.

Now you need to know how many fish that is.

From the feed conversion mentioned earlier, we know that two pounds of fish food yield one pound of fish.

Convert grams to divide by 454 to pounds.

  • 8,190 / 454 = 18 pounds of fish food.

Now divide it by the FCR (feed conversion rate) of 2.

  • 18/2 = 9 pounds of fish.

Growing them to a pound can store 9 fish (9/1). If you grow them to a pound and a half you can keep 6 fish (9 / 1.5) in stock.

Tilapia needs two litres of water per pound of fish. This is different for every fish species. Trout, for example, needs 8 gallons per pound. Going with the example of tilapia, you will need a minimum 18-gallon aquarium. Tilapia grows better in densely populated tanks because they won’t chase each other and get stressed out.

2. Fish/plant ratio in DWC or NFT

To calculate the fish to plant ratio on deep water culture or NFT, you must change the feed rate.

Why do you need an optimal ratio between fish and plants?

Every aquaponist may want to maximize their return on investment (ROI) on fish and plant in the shortest amount of time with the least possible risk. For a more efficient aquaponics system, you must maintain the optimal balance between the production of nutrients from the fish culture and the absorption of nutrients by the plant.

Water quality for fish growth

The highly toxic ammonia and nitrites produced from fish waste must be removed. The high nitrite content can cause nitrate poisoning in the aquarium and kill the fish. The plants act as a biofilter that must be large enough to process all fish waste and filter the water.

Fewer plants can grow well, but they may not be able to efficiently remove contaminants from the water. You can eventually reduce the fish food to reduce waste, which leads to slower fish growth. Otherwise, poor water quality (nitrate / nitrite levels, DO, etc.) will also lead to poor feed conversion (FCR).

Nutrient for plant growth

In aquaponics, plants thrive on nutrients produced from fish waste. There must be enough fish and enough food to provide the plants with the correct nutrients.

A higher plant density results in inadequate water quality and good fish production without the exchange of large amounts of water or complex biofiltration equipment.

Factors influencing the relationship

Every aquaponics system manufactured is necessarily different in terms of many factors, i.e. fish species, plant selection, system size, design. You should be aware of the effect of the following different factors on fish and plant growth. This will ultimately lead to the optimal fish to plant ratio for your aquaponics system.

Feed rate

Firstly, let’s analyze the most important factor and the one that directly affects. The ratio of fish to plant is directly dependent on the feed rate in a well-maintained aquaponic system. In general, fish use about 80% of their food and excrete the remaining 20% ​​as waste.

The amount of food fed to the fish daily is taken into account per square meter of plant culture area. In general, 100 grams of fish food supports about a square meter of plant life. The optimal feeding rate ratio also depends on several factors, such as the type of breeding bed, the type of plant and the fish species. The NFT system requires approximately 25% of the feed rate used for a float system.

Choice of plants

The concentration of nutrients that plants need largely depends on the type. Different plants have different nutritional needs.

Plants that require low to medium nutrition include lettuce, herbs, onion, cabbage, cauliflower, garlic, peas, and especially green vegetables (spinach, chives, basil, etc.).

Flowering and fruiting plants such as tomatoes and cucumbers have higher nutritional requirements. They need a well stocked and established aquaponic system to grow best. If you grow indoors, they also require full spectrum LED grow lights for their vegetative and flowering phase.

Fish species

The fish you will be keeping is an important step in setting up your aquaponics system as it has a long-lasting impact. Any fish tends to produce waste that provides ammonia and nutrients to plants.

However, some fish, such as trout, require high quality water and you will need to grow more plants to minimize wastage in the water. Some species like tilapia can tolerate poor quality water and can be stocked at higher densities. Any native fish that can accept food is a good choice.

Population densities

Population densities refer to the amount of fish that you have kept in your system. You cannot keep more than a specific amount of fish in the aquaponics system. Otherwise, the fish may even die due to low dissolved oxygen, high nitrite, or just kill each other due to territorial behaviour. Some fish like tilapia reproduce quickly and can exceed one system. The total length of the fish is considered for the population density rather than the number of fish.

You must manage the fish population based on their size and feeding requirements. A handful of goldfish on your aquaponic farm need less feed, but that will result in less plant growth. You will also need to sync and consider the requirements of the plants after harvesting the fish (and vice versa).

System type and age

System maturity is very important for a sustainable aquaponics system. To start an aquaponics system, you must first cycle your fish tank.

The balance to maintain the fish-to-plant ratio is difficult to achieve in a new system. In general, it is a good practice to start with a smaller amount of fish. Then increase the population as your plants grow or make sure the fish grow at the same rate to provide enough plant nutrients. This way, you will also have a better idea of ​​your surroundings.

Larger fish consume more food and produce more fertilizer waste. The size and type of aquaponic setup (grow bed, DWC, or vertical) are also important as it indicates the ability of the system to convert fish waste (ammonia) to nitrites and then nitrates (plant food). The more surface area your culture beds have, the more fish you can transport, as they harbor your colony of bacteria that does all the work.

In an established system, it will eat fish that reach the size of a plate and plants throughout the season as it grows. You must maintain the ratio between plants and fish to ensure a balance of the working system.

Your choice

Your choice impacts a lot in the end. Some like more fish and others more plants. Those who want more fish than vegetables would use filters or some kind of RAS approach. Some use goldfish and don’t eat fish at all.

There is no single optimal ratio for every combination or type of system, fish, and plant. Then you will play with the factors mentioned above to achieve the ratio you want! So let’s take a look at the optimal fish to plant ratio.

What is the optimal temperature range for aquaponics?

Temperature is an important parameter in aquaponics, and as we all know, there are 3 main players in Aquaponics which are:

  • Fish
  • Plants
  • Bacteria

Water temperature affects all components and aspects of aquaponic systems. In general, a common compromise range is 68-86 ° F (20-30 ° C). The temperature affects both the DO content and the toxicity (ionization) of ammonia; the rise in temperature lowers the levels of DO and increases the union of (toxic) ammonia.

Let’s see how temperature affects

The 64 – 86 ° F (18 – 30 ° C) temperature range is ideal for most vegetables. However, a few vegetables are much more suitable for growing under certain conditions.

Many chilled vegetables such as lettuce, chard, and cucumbers grow better in temperatures of 8–20 ° C. While in warm weather vegetables such as okra, cabbage, and basil need a temperature of 63-86 ° F (17-30 ° C). At temperatures above 79 ° F (26 ° C), leafy greens begin to bolt and produce seeds and flowers, making them unsaleable and bitter.

So the first rule is to make sure you grow vegetables according to their season. Season and environment also affect the water of the aquaponics system. That can affect the plants’ ability to absorb nutrients and grow.

Your ability to control water temperature largely depends on where you grow the plants. It is more difficult to maintain the environment if you grow outside or in a warm/cold cellar.

The soil naturally insulates the heat for the plants that grow in the ground.

If you dig a hole more than a foot deep, you will realize how moist and cool it is down there compared to the surface. The roots are comfortable and naturally live in that environment. Exposure of the roots to conditions that are uncomfortable for them puts stress on the plant.

In aquaponics, the water temperature has more influence on the plants than on the air temperature.

1. Problems due to high water temperatures

The rise in water temperatures will lead to heat stress in the plants. The plant closed its roots and eventually went into survival mode when exposed to high water temperatures.

Some symptoms of heat stress include

  • Low dissolved oxygen content
  • Wilting
  • Soft brown spots on fruit
  • Plants begin to drop flowers and break down fruiting bodies
  • The roots are starting to get slimy
  • Lettuces plants start to sprout (grow taller and reach seed)
  • Limit the ability to absorb calcium in plants.
  • The roots turn black and die

The severity of heat stress in plants is also affected by the temperature and humidity of the air.

2. Problems due to cold water temperatures

Although the cold nutrient solution is usually not a problem, it can cause some problems when growing.

  • Outdoors during the winter, fall, or early spring
  • In a basement, cellar, garage, etc.

Low temperatures have only one major drawback. The colder temperature slows down plant growth. The severity depends on the duration of the exposure and the temperature of the water.

You may notice a reduced growth rate when the water temperature drops below 60 ° F (15 ° C). Since the air temperature strongly affects the water temperature, the temperatures of the reservoir are generally cold due to the cold season. The combination of cold air and reservoir temperature results in very slow growth. Due to colder nighttime temperatures, it still takes much longer for the plant to wake up, even during the day when the air around the water gets warmer.

Temperature and fish

Cold-blooded fish are less able to adapt to varying water temperatures.

The fish can also be divided into cold water, warm water, and cool water fish. In general, tropical fish (e.g. catfish, carp, and tilapia) thrive in waters with higher temperatures of 22 to 32 ° C. However, cold-water fish such as trout prefer ranges between 10 and 18 ° C. between 5 and 30 ° C. There are many factors to consider when choosing your fish, along with the temperature.

A stable temperature within the correct tolerance range

  • Minimize the risk of illness
  • Keeps fish in optimal conditions
  • Helps with faster growth
  • Facilitate and efficient feed conversion.

The appetite of fish, especially tropical fish such as tilapia, is also directly related to water temperature. So make sure to adjust and reduce your diet during the winter season.

The increase in temperature improves the respiratory rate and metabolism, as well as the oxygen demand of the fish, approximately doubling respiration for a temperature increase of 10 ° C. Therefore, it can be said that the oxygen demand increases due to a lower oxygen supply. Raising the temperature increases the solubility of many toxic substances.

You can use thermal insulation, water heaters, and coolers to achieve the desired temperature level, although this can increase operating costs in areas where energy is expensive. It is always best to have fish that are adapted to the local environmental conditions.

Nitrifying bacteria

Water temperature is an essential part of bacteria and for aquaponics in general. The optimal temperature range for bacterial growth and productivity is 17 to 34 ° C. The growth rate decreases by 50% at 64 ° F (18 ° C) and by 75% at 46-50 ° F. No activity takes place at 39 ° F (4 ° C). Temperature levels below 32 ° F (0 ° C) or above 120 ° F (49 ° C) kill nitrifying bacteria. Low-temperature levels have a significant impact on the management of the system during the winter.

Overlying temperature

The optimal temperature for aquaponics is

  • Root zone temperature = 22 ° C
  • Fish temperature = 10-32 ° C
  • Bacteria and nitrification = 25-30 ° C

The general temperature range is 20-30 ° C, which must be adapted to the species of fish or plant. Bacteria thrive in this temperature range. It is important to choose a suitable combination of plant and fish species that are well adapted to each other and to the environmental conditions.

If the temperature is too high:

Plants will wither and die, some fish will eat more food and therefore increase ammonia/nutrients, because higher temperatures reduce the solubility of dissolved oxygen and therefore reduce the availability of this essential gas.

If the temperature is too low:

Slower plant growth, bacteria no longer work and some fish may not eat

Recommendations

Choose the right types of fish and plants carefully to meet your optimal water temperature needs.

  1. Choose plants and fish that are already adapted to the local climate. However, there are management techniques that can minimize temperature fluctuations and extend the growing season.
  1. Protect the water surface itself, in all water tanks and units, from the sun by means of shade structures. Because systems are more productive when daily temperature changes, from day to night, are minimal.
  1. In the same way, you can thermally protect the appliance by using insulation at night against low temperatures. Alternatively, you can use greenhouses or solar panels with agricultural rolled pipes to heat the aquaponic units passively, practically ideal for temperatures below 15 ° C;
  1. When choosing fish, consider the seasons of vegetables.

Conclusion

The fish and plants you select for your aquaponic system should have similar needs for temperature and pH. There will always be a compromise with the needs of fish and plants, but the more they match, the more successful you will be. Therefore, keep your fish in the best possible environment and they will always produce a beautiful product.

Lindsey Glenn

I've been learning about gardening since 2015, helping friends and family to grow their trees. I am passionate about trees and love sharing everything I learn about them.

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