3.3. Biotic Components of Aquaponic Systems

The biotic components of aquaponic systems consist of plants, fish (aquatic organisms), and bacteria. Understanding the contribution of each component to system functionality, the selection criteria for these components, and their respective roles within the system is crucial for ensuring the efficiency and sustainable development of aquaponic systems. In aquaponic setups, specific plant and fish species can be cultivated together. Selecting the appropriate combination of plant and fish species is essential for efficient system operation and continuous production. In a well-designed aquaponic system, the organic load in the water can be utilized effectively, water consumption can be minimized, and the profitable production of both fish and plants can be achieved. Therefore, fish and plant species selection should be made by considering all system dynamics to maximize productivity. Information regarding the selection criteria of fish and plant species, as well as the roles of bacteria in aquaponic systems, is presented in the following sections.

3.3.1. Fauna Cultivated in Aquaponics and Fish Selection Criteria

The fauna cultivated in aquaponic systems serve as the primary nutrient source for the system. When selecting fish species for aquaponic systems, several system-related criteria must be considered.These include factors such as the water temperature that the established aquaponic system can maintain, the stocking density the system can support, the legally permitted and economically viable species in the country where the system is operated, and the market demand for certain fish species (Gökvardar et al., 2022). Figure 1 summarizes the main criteria for selecting fish species preferred in aquaponic systems.

 

Figure 1. Fish Selection Criteria in Aquaponics (Gökvardar et al., 2022)

Tilapia, Catfish, Trout, and Carp are reported to be the most commonly preferred fish species by aquaponic producers (Bildirici & Bildirici, 2021). Among these, Tilapia (Oreochromis sp.) is the most widely used species in aquaponic studies due to its ability to thrive at relatively high water temperatures (around 23.5 °C) and its rapid growth rate (Gökvardar et al., 2022). It has been reported that Tilapia can reach a body weight of approximately 1 kg within eight months under optimal conditions (Martins et al., 2009). Tilapia species are also known for their tolerance to high suspended solid concentrations and low dissolved oxygen levels in water (Bildirici & Bildirici, 2021). Another significant advantage of Tilapia over other species is its high resistance to diseases and parasites (Gökvardar et al., 2022). Feeding Tilapia with high-protein feeds contributes to higher nitrate levels in the system, which in turn supports plant growth in the aquaponic environment (Tunçelli, 2024). According to the literature, Tilapia diets should contain approximately 30% protein (Özçiçek, 2023a).Furthermore, due to its ability to be stocked at high densities, Tilapia farming allows the nutrient requirements of plants in the aquaponic system to be effectively met (El-Sayed, 2006). Commercially, the main Tilapia species preferred in aquaponic production are Blue Tilapia (Oreochromis aureus), Nile Tilapia (Oreochromis niloticus), and Mozambique Tilapia (Oreochromis mossambicus) (Somerville et al., 2014).

Catfish are preferred in aquaponic systems due to their rapid growth rate, tolerance to variable water temperatures and dissolved oxygen levels, and ability to consume a wide variety of feed types (Tunçelli, 2024). The main catfish species cultivated for commercial aquaponic production are Channel Catfish (Ictalurus punctatus) and African Catfish (Clarias gariepinus) (Özçiçek, 2023a). Catfish can thrive in warm water conditions, typically around 26 °C (Özçiçek, 2023a). Since catfish are bottom-dwelling species that develop along the tank floor, they are often cultivated together with surface-dwelling species such as bass or tilapia in multi-species aquaponic systems (Somerville et al., 2014).

Trout, a cold-water fish species, is highly valued by consumers for its flavor and nutritional content.Its high levels of vitamin A, vitamin D, and omega-3 fatty acids make it a particularly healthy and desirable option for consumers (Somerville et al., 2014).Trout are sensitive to changes in temperature and water quality (Tunçelli, 2024).According to information obtained from rainbow trout producers, high dissolved oxygen concentrations are essential for successful cultivation of this species.In trout farming, the optimal dissolved oxygen level should be above 6 mg/L (Somerville et al., 2014).The main trout species preferred for commercial aquaponic production is the Rainbow Trout (Oncorhynchus mykiss) (Somerville et al., 2014), which thrives at optimal water temperatures of 17–18 °C (Özçiçek, 2023a).

Carp are among the most frequently preferred species in aquaponic systems.
The main carp species cultivated for commercial aquaponic production are Common Carp (Cyprinus carpio), Silver Carp (Hypophthalmichthys molitrix), and Grass Carp (Ctenopharyngodon idella) (Somerville et al., 2014).Carp are favored by aquaponic producers due to their broad temperature tolerance, being able to survive within a range of 4 °C to 34 °C, and their resistance to variable water quality conditions (Özçiçek, 2023a).Koi Carp, which also hold significant economic value, are mainly cultivated for the ornamental fish industry (Özçiçek, 2023a).Figure 2 summarizes the most preferred and commercially important fish species cultivated in aquaponic systems.

 

Figure 2. Commonly Preferred Fish Species in Aquaponics

3.3.2. Plant Species, Selection, and Cultivation in Aquaponics

Plants used in aquaponic systems serve as a biological filter, facilitating nutrient recovery from the wastes generated by aquatic organisms cultivated within the system. The preferred plant species in aquaponic systems are those that have a high nitrogen demand, can be grown rapidly, are economically viable, and are popular among consumers (Bailey & Ferrarezi, 2017; Özçiçek, 2023b).The primary factor to consider when selecting plant species for aquaponic systems is the stocking density of the fish tanks and the nutrient concentration in the effluent water (Özçiçek, 2023b).

In the selection of plant species for aquaponic systems, the type of aquaponic technique applied is also taken into consideration. In this context, the media bed technique allows for the simultaneous cultivation of multiple plant species, whereas the nutrient film technique (NFT) and the deep water culture (DWC) technique are generally used for the cultivation of a single plant species (Özçiçek, 2023b).

Another important factor to consider when selecting plant species in aquaponic systems is the nitrogen cycle within the system. In this context, plant species are selected based on their nitrogen uptake capacity and the ability of nitrifying bacteria to adhere to the root surface area of the plants (Özçiçek, 2023b). A larger root surface area allows a greater number of nitrifying bacteria to attach, thereby enhancing nitrogen recovery and increasing the amount of nitrogen available for plant uptake (Hu et al., 2015). In addition, the climatic conditions of the country where the aquaponic system is established and the market demand for specific crops are also key factors influencing plant selection (Özçiçek, 2023b). Figure 3 summarizes the main factors considered in plant selection for aquaponic systems.

 

Figure 3. Plant Selection Criteria in Aquaponics

In aquaponic systems, various plant types can be cultivated, including leafy vegetables such as lettuce, spinach, arugula, and cabbage; fruiting vegetables such as tomatoes, cucumbers, and peppers; fruits such as strawberries and blackberries; and aromatic herbs such as basil, mint, thyme, and parsley. Among these, lettuce, basil, tomato, and mint are the most commonly preferred plant species in aquaponic systems (Tunçelli, 2024). Figure 4 provides a visual summary of the most commonly cultivated plant species in aquaponic systems.

 

Figure 4. Commonly Preferred Plants in Aquaponics

Lettuce (Lactuca sativa) is one of the most commonly cultivated plants in aquaponic systems due to its low maintenance requirements and rapid growth rate. Different varieties such as iceberg lettuce, butterhead lettuce, and loose-leaf lettuce can be successfully grown in aquaponic setups (Somerville et al., 2014). In aquaponic lettuce cultivation, the Deep Water Culture (DWC) and Nutrient Film Technique (NFT) methods are generally used (Tunçelli, 2024). Lettuce requires high levels of nitrogen during its growth period. It is a fast-growing plant species that can be cultivated in all regions of Türkiye, has high market demand, and shows excellent compatibility with aquaponic production (Kandemir & Bayındır, 2019; Özçiçek, 2023b). Lettuce grows well under temperature conditions of 15–22 °C (Somerville et al., 2014), and slightly acidic to neutral pH levels in aquaponic water are considered optimal for its cultivation (Ware, 1980). Figure 5 presents an image of lettuce plants grown in an aquaponic system.

 

Figure 5. Lettuce Cultivation in Aquaponics

Mint is a fast-growing plant species that can be cultivated in various types of aquaponic systems, including media bed, deep water culture (DWC), and nutrient film technique (NFT) systems (Tunçelli, 2024). Basil (Ocimum basilicum), which belongs to the same botanical family as mint, is an aromatic herb with high economic value that is commonly cultivated in large-scale aquaponic systems using media bed and nutrient film techniques (Somerville et al., 2014; Özçiçek, 2023b; Tunçelli, 2024).
Basil thrives at temperatures between 20–25 °C and is widely grown in tropical and temperate regions (Ceylan, 1997; Özçiçek, 2023b). In addition to its uses as a culinary spice, food ingredient, pharmaceutical plant, and ornamental herb, basil also presents a significant potential for essential oil production (Shahrajabian et al., 2020).

Tomato (Lycopersicon esculentum), classified as a fruiting plant, is a species with a high nitrogen requirement that must be cultivated under controlled environmental conditions, particularly with attention to light intensity and pH levels in the water (Tunçelli, 2024). It has been reported that the cultivation of flowering plants in aquaponic systems requires more delicate maintenance compared to leafy vegetables, as these plants have higher phosphorus and potassium demands (Rakocy, 2012; Bildirici & Bildirici, 2021). In tomato cultivation, daytime temperatures should be maintained between 21–29 °C and nighttime temperatures between 18–20 °C (Peirce, 1987).
Additionally, the optimal pH range for tomato cultivation in aquaponic systems is 5.5–6.5 (Özçiçek, 2023b). Figure 6 presents an image of tomato plants grown in an aquaponic system.

 

Figure 6. Tomato Grown in an Aquaponic System

In aquaponic plant cultivation, plants should be maintained at different growth stages within the production cycle to enable staggered harvesting. This approach ensures that the nutrient demand in the system remains stable over time (Özçiçek, 2023b). Maintaining plants at various growth phases contributes to stable water quality while allowing for continuous production (Somerville et al., 2014).

3.3.3. Bacteria in Aquaponics and Their Functions

In aquaponic systems, bacteria play an active role in converting materials contained in fish waste and uneaten feed residues into bioavailable forms for plants, thereby playing a crucial role in the nutrient recovery process.
According to the literature, fish feed generally contains approximately 6–8% organic nitrogen, 6–8% macronutrients, 1.2% organic phosphorus, and 40–45% organic carbon (Timmons & Ebeling, 2010; Bildirici & Bildirici, 2021).
The composition of wastewater released from the fish tank is directly proportional to the composition of the feed used to nourish the fish.

Among the bacteria functioning in aquaponic systems, the most important are the nitrifying bacteria. These microorganisms play a vital role in the nitrogen cycle, ensuring the continuity and efficient operation of the system (Bingöl, 2019). The primary sources of nitrogen in aquaponic systems are fish excreta and uneaten feed residues, both of which have high nitrogen content. After fish consume the feed, ammonia (NH₃/NH₄⁺) is released as a nitrogenous waste product. Since ammonia is toxic to fish, the role of bacteria in the cycle becomes crucial. Nitrifying bacteria, primarily Nitrosomonas and Nitrobacter species, convert ammonia first into nitrite (NO₂⁻) and then into nitrate (NO₃⁻)—a form that can be readily absorbed by plants (Kim et al., 2005). Thus, these bacteria transform toxic nitrogen compounds into safe nutrients, while plants absorb the nitrate through their roots for growth, simultaneously purifying the water and maintaining a healthy environment for the fish. Nitrifying bacteria are predominantly concentrated near the biofilter unit within the system (Bildirici & Bildirici, 2021). For the nitrification process to occur effectively, the system should maintain a temperature between 25–30 °C and a pH range of 7–9 (Antoniou et al., 1990).

In aquaponic systems, phosphorus, like other essential minerals, primarily originates from fish feed and fish metabolism, being excreted through feces. However, the phosphorus released into the system is mainly in organic forms, and therefore must be converted into inorganic phosphate (PO₄³⁻) before it can be directly utilized by plants (Becquer et al., 2014). At this point, heterotrophic microorganisms involved in phosphorus mineralization play a critical role by converting organic phosphorus into inorganic phosphate (PO₄³⁻) (Joyce et al., 2019), making phosphorus bioavailable for plants. Several studies have identified bacterial genera such as Bacillus, Klebsiella terrigena, Escherichia coli, Pseudomonas sp., Roultella sp., Citrobacter braakii, and Enterobacter as microorganisms capable of degrading phytate, one of the most common organic forms of phosphorus in aquaponic systems, thereby releasing inorganic phosphate (PO₄³⁻) (Riaño-Castillo et al., 2024).

 

The conversion and recovery of phosphorus into plant-available forms in aquaponic systems reduces the need for external phosphorus supplementation, since phosphorus is the second most essential macronutrient for plants after nitrogen (Joyce et al., 2019). However, excessive accumulation of phosphorus in the system may lead to algal growth and water quality deterioration, making phosphorus uptake by plants crucial for maintaining the ecological balance of the cycle.

In a study investigating the bacterial community composition in an aquaponic system, samples were collected from the plant roots in the hydroponic unit and the water in the biofilter compartment for bacterial community analysis (Prastowo et al., 2024). According to the results, the root surfaces of the plants were predominantly colonized by the bacterial phylum Proteobacteria (76%), while the biofilter compartment of the aquaponic system was mainly inhabited by members of the Bacteroidota (71%) phylum, particularly the Flavobacterium and Cloacibacterium genera. It has been reported that the Proteobacteria community contributes significantly to the nitrification process occurring in soil and aquatic environments, while the Flavobacterium genus plays an important role in the decomposition of complex organic matter, and the Cloacibacterium genus contributes notably to the nitrogen cycling of waste in aquatic environments (Waśkiewicz et al., 2014; Eck et al., 2019; Prastowo et al., 2024).

 

 

 

 

 

 

 

 

 

 

Reference

Antoniou, P., Hamilton, J., Koopman, B., Jain, R., Holloway, B., Lyberatos, G., & Svoronos, S. A. (1990). Effect of temperature and pH on the effective maximum specific growth rate of nitrifying bacteria. Water Research, 24(1), 97-101.

Bailey, D. S., & Ferrarezi, R. S. (2017). Valuation of vegetable crops produced in the UVI Commercial Aquaponic System. Aquaculture Reports, 7, 77-82.

Becquer A, Trap J, Irshad U, Ali MA, Claude P (2014) From soil to plant, the journey of P through trophic relationships and ectomycorrhizal association. Front Plant Sci 5:548

Bildirici, N., & Bildirici, D. E. (2021). Sağlıklı bir gelecek için aquaponik sistemler. Ankara: Iksad Publications.

Bingöl, B. 2019. Alternatif Tarım Yöntemleri; Aeroponik, Akuaponik, Hidroponik. Harman Time Dergisi, Aralık/2019, 7(82), 34-42, ISSN: 2147-6004.

Ceylan, A. (1997). Tıbbi Bitkiler-II (uçucu yağ bitkileri). İzmir: Ege Üniversitesi Ziraat Fakültesi, No: 481.

Eck, M.  Sare, A.R.  Massart, S.  Schmautz, Z.  Junge, R.  Smits, T.H.M. Jijakli, M.H. 2019,  Exploring bacterial communities in aquaponic systems, Water (Switzerland) 11 (2) https://doi.org/10.3390/w11020260.

El-Sayed, A. F. M. (2006). Tilapia Culture. CABI eBooks. Oceanography Department, Faculty of Science, Alexandria University, Alexandria, Egypt.

Gökvardar, A., Özden, O., Serezli, R. (2022). Su Ürünleri Yetiştiriciliğinde Sürdürülebilir Uygulamalar: Akuaponik Sistem Yaklaşımları. In B. Karataş (Ed.), Su Ürünlerinde Modern Perspektifler (Bölüm 2, ss. 25-58). Ankara: Iksad Publications.

Hu, Z., Lee, J. W., Chandran, K., Kim, S., Brotto, A. C. & Khanal, S. K. (2015). Effect of plant species on nitrogen recovery in aquaponics. Bioresource Technology, 188, 92-98.

Joyce, A., Timmons, M., Goddek, S., Pentz, T., 2019. Bacterial Relationships in Aquaponics: New Research Directions. In: Goddek, S., Joyce, A., Kotzen, B., Burnell, G.M. (Eds.), Aquaponics Food Production Systems: Combined Aquaculture and Hydroponic Production Technologies for the Future. Springer International Publishing, Cham, pp. 145-161. https://doi.org/10.1007/978-3-030-15943-6_2, 978- 3-030-15943-6.

Kandemir, D. & Bayındır, S. (2019). Yetiştirme Tekniği. Marul Tarımı (Özel Sayı). Tarım Gündem Dergisi, ISBN:978-605-7846-39-6.

Kim, D.-J., Ahn, D.H., Lee, D.-I., 2005. Effects of free ammonia and dissolved oxygen on nitrification and nitrite accumulation in a biofilm airlift reactor. Korean J. Chem. Eng. 22, 85–90.

Martins, I. M., Ochola, D., Ende, S. W., Eding, H. E. & Verreth, J. A. (2009). Is growth retardation present in Nile tilapia Oreochromis niloticus cultured in low water exchange recirculating aquaculture systems? Aquaculture, 298 (1-2), 43-50.

Özçiçek, E. (2023a). Akuaponik Sistemlerde Önemli Balık Türleri. In H. Y. Çoğun (Ed.), Su Ürünlerinde Yeni Gelişmeler (Bölüm 2, ss. 47-62). Ankara: BİDGE Yayınları

Özçiçek, E. (2023b). Akuaponik Sistemlerde Önemli Bitki Türleri. In H. Y. Çoğun (Ed.), Su Ürünlerinde Yeni Gelişmeler (Bölüm 2, ss. 117-131). Ankara: BİDGE Yayınları

Peirce, L. C. (1987). Vegetables: characteristics, production, and marketing. Toronto: John-Wiley & Sons. Inc.

Prastowo, B.W., Lestari, I.P., Agustini, N.W.S, Priadi, D., Haryati, Y.,  Jufri, A., Deswina, P. Adi, E.B.M., Zulkarnaen,I., 2024. Bacterial communities in aquaponic systems: Insights from red onion hydroponics and koi biological filters, Case Studies in Chemical and Environmental Engineering, 10, 100968.  https://doi.org/10.1016/j.cscee.2024.100968.

Rakocy, J. E., Masser, M. P. & Losordo, T. M. (2006). Recirculating aquaculture tank production systems: aquaponics – integrating fish and plant culture. Southern Regional Aquaculture Center. USA: SRAC Publication, No. 454.

Riaño-Castillo, E.R.; Rodríguez-Ortiz, J.C.; Kim, H.-J.; Guerrero González, M.d.l.L.; Quintero-Castellanos, M.F.; Delgado-Sánchez, P. Isolation and Identification of Lysinibacillus sp. And Its Effects on SolidWaste as a Phytate-Mineralizing Bacterium in an Aquaponics System. Horticulturae 2024, 10, 497. https://doi.org/10.3390/horticulturae10050497

Shahrajabian, M. H., Sun, W. & Cheng, Q. (2020). Chemical components and pharmacological benefits of basil (Ocimum basilicum): a review. International Journal of Food Properties, 23 (1), 1961–1970.

Somerville, C., Cohen, M., Pantanella, E., Stankus, A. & Lovatelli, A. (2014). Small-scale aquaponic food production.Integrated fish and plant farming. Rome: FAO Fisheries and Aquaculture Technical Paper. No. 589.

Timmons, M.B. & Ebeling, J.M. (2010). Recirculating Aquaculture, 2nd ed. NRAC Publication NO. 01-007. Cayuga Aqua Ventures, Ithaca, NY.

Tunçelli, G. (2024). Su Ürünleri Yetiştiriciliğine Yenilikçi Yaklaşımlara Örnek: Akuaponik Sistemler. Tarım Ve Mühendislik Dergisi, 57-65.

Ware, G. W. (1980). Effects of pesticides on nontarget organisms. In: F. A. Gunther, J. D. Gunther (Ed.), Residue Reviews (pp. 173-201). New York: Springer New York.

Waśkiewicz, A., & Irzykowska, L. (2014). Flavobacterium spp. – Characteristics, Occurrence, and Toxicity. Encyclopedia of Food Microbiology, 938–942. https://doi.org/10.1016/B978-0-12-384730-0.00126-9