Management of the aquaponic systems Source Fisheries and Aquaculture Department (FI) in FAO Keywords Aquaculture, aquaponics, fish, hydroponics, soilless culture Country of first practice Global ID and publishing year 8398 and 2015 Sustainable Development Goals No poverty, industry, innovation and infrastructure, and life below water Summary Aquaponics is the integration of recirculating helpful calculations to estimate the sizes of aquaculture and hydroponics in one each of the components. The ratio estimates production system. Although the production how much fish feed should be added each of fish and vegetables is the most visible day to the system, and it is calculated based output of aquaponic units, it is essential on the area available for plant growth. This to understand that aquaponics is the ratio depends on the type of plant being management of a complete ecosystem that grown; fruiting vegetables require about includes three major groups of organisms: one-third more nutrients than leafy greens fish, plants and bacteria. This document to support flowers and fruit development. provides recommendations on how to keep The type of feed also influences the feed a balanced system through the proper rate ratio, and all calculations provided here management of these three organisms. It assume an industry standard fish feed with also lists all the important management 32 percent protein (Table 1). phases from starting a unit to production Table 1: Daily fish feed by plant type management over an entire growing season. Leafy green plants Fruiting Vegetables Description 40 to 50 g of fish 50 to 80 g of fish 1. System balance feed per square feed per square This technology covers basic principles meter meter Source: FAO 2015 and recommendations while installing a new aquaponic unit as well as the routine On average, plants can be grown at management practices of an established the following planting density. This will system. Aquaponic systems need to be ensure that the plants have adequate balanced. The fish (and thus, fish feed) need nutrients. Overly dense planting will lead to to supply adequate nutrients for the plants. deficiencies and too low densities will not The plants need to filter the water for the adequately filter the water. These figures fish. The biofilter needs to be large enough are only averages, and many variables exist to process all of the fish wastes, and enough depending on plant type and water volume is needed to circulate this harvest size, and therefore system. This balance can be tricky to achieve should only be used as TECA in a new system, but this section provides guidelines (Table 2). TECHNOLOGIES and PRACTICES for SMALL AGRICULTURAL 1/10 PRODUCERS Fishery and Aquaculture Table 2: Planting density by plant type more complex filtration system to deal with the solid waste (Table 4). Leafy green plants Fruiting Vegetables Table 4: Fish stocking density 20 to 25 g of fish 4 plants per square feed per square meter Fish stocking density meter 10 to 20 kg of fish per 1 000 litre of water Source: FAO 2015 Source: FAO 2015 On average, the fish will consume 1 to Table 5 summarizes the key figures and ratios 2 percent of their body weight per day during for designing small-scale media bed, NFT and the grow-out stage. This assumes that the DWC units. It is important to be aware that fish are larger than 50 g because small fish the figures are just guides as other external eat more than large ones, as a percentage of factors (climate conditions, access to a body weight (Table 3). constant supply of electricity for example) Table 3: Fish feeding rate may change the design on the ground. Please Fish feeding rate note the footnotes below explaining the 1 to 2 percent of total body weight per day figures and the applicability of each column per aquaponic method. Source: FAO 2015 The recommended maximum stocking • The recommended fish density is based on density is 20 kg of fish for 1 000 litres of a maximum stocking density of 20 kg per water (fish tank). The small-scale units 1 000 litres. Higher densities are possible described in this publication have about with further aeration and mechanical 1 000 litres of water and should contain 10 to filtration, but this is not recommended for 20 kg of fish. beginners. • The recommended feeding rate is Higher stocking densities require more 1 percent of body weight per day for fish sophisticated aeration techniques to keep of more than 100 g of body mass. The the DO levels stable for fish, as well as a feeding rate ratio is 40 to 50 g per m² for Table 5: Practical system design guide for small scale units Fish tank Max. fish Pump Filter Min. volume of Feed rate Plant growing volume biomass flow rate volume biofilter media (g/day) area (m2) (Litre) (kg) (litre/h) (litre) (litre) Volcanic Bioballs Tuff 200 5 50 800 20 50 25 1 500 10 100 1 200 20-50 100 50 2 1 000 20 200 2 000 100-200 200 100 4 1 500 30 300 2 500 200-300 300 150 6 2 000 40 400 3 200 300-400 400 200 8 3 000 60 600 4 500 400-500 600 300 12 Source: FAO 2015 2/10 leafy greens; and 50 to 80 g per m² for the plants. This is a two-step process, and fruiting vegetables. two separate groups of nitrifying bacteria are • The volumes for mechanical separator involved as shown in Figure 1. Therefore a and biofilter should be 10 to 30 percent of good establishment of the bacteria colony is total fish tank volume. In reality, the choice crucial for a new aquaponic system. of containers depends on their size, cost System cycling is a term that describes the and availability. Biofilters are only needed initial process of building a bacterial colony for NFT and DWC units. Mechanical when first starting any aquaponic unit. separators are applicable for NFT, DWC Under normal circumstances this takes three units and media bed units with a fish to five weeks as cycling is a slow process density of more than 20 kg per 1 000 litres. that requires patience. Overall, the process • These figures assume the bacteria are in involves constantly introducing an ammonia optimal conditions all the time. If not, for source into the aquaponic unit, feeding the a certain period (winter), extra filtration new bacterial colony, and creating a biofilter. media may need to be added as a buffer. The progress is measured by monitoring the Different values are provided for the two nitrogen levels using the nitrate test kit. most common biofilter media based on their respective specific surface area. Once introduced into the unit, the ammonia • Figures for plant growing space include becomes an initial food source for the only leafy greens. Fruiting vegetables ammonia-oxidizing bacteria (AOB), a few would have a slightly lower area. of which are naturally occurring and recruit to the system on their own. They can be In addition, daily health monitoring of the found on land, in water and in the air. Within fish and the plants will provide feedback five to seven days after the first addition of on the balance of the system. Disease, ammonia, the AOB start forming a colony nutritional deficiencies and death are and begin to oxidize the ammonia into symptoms of an unbalanced system. Water nitrite. Ammonia should be continuously, but testing will provide information on the cautiously, added to ensure adequate food balance of the system. High ammonia or for the developing colony without becoming nitrite indicates insufficient biofiltration. toxic. After another five to seven days the Low nitrate indicates too many plants or not nitrite levels in the water will have started to enough fish. Increasing nitrate is desirable rise, which in turn attracts the NOB. As the and indicates adequate nutrients for the Nitrite-oxidizing Bacteria (NOB) populations plants, though water needs to be exchanged increase, the nitrite levels in the water will when nitrate is greater than 150 mg per litre. start to decline as nitrite is oxidized into 2. System cycling and starting a biofilter nitrate. The end of the cycling process is colony defined as when the nitrate level is steadily Bacteria are a crucial and pivotal aspect increasing, the nitrite level is 0 mg per litre of aquaponics, serving as the bridge that and the ammonia level is less than 1 mg per connects the fish waste to the plant fertilizer. litre. In good conditions, this takes about The nitrifying bacteria convert the fish 25 to 40 days, but if the water temperature waste, which enters the system mainly as is cool, complete cycling may take up to two ammonia, into nitrate, which is fertilizer for months to finish. At this point, a sufficient 3/10 bacterial colony has formed and is actively Figure 2. Levels of ammonia, nitrite and nitrate during the converting the ammonia to nitrate. first few weeks in a recirculating aquaculture system The reason this process is long is because nitrifying bacteria grow relatively slowly, requiring 10 to 15 hours to double in population. However, some heterotrophic bacteria can double in as little as 20 minutes. Alternatively, if another aquaponic system is available, it is extremely helpful to share part of the biofilter as a seed of bacteria for the new system. This greatly decreases the time necessary for cycling the system. It can also be useful to separately start a biofilter © FAO/TECA medium by continuously trickling a solution 3.1 Establishing a plant nursery containing 2 to 3 mg per litre of ammonia Vegetables are the most important output for a few weeks in advance.